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Revision 1.94 by root, Fri Dec 21 04:38:45 2007 UTC vs.
Revision 1.229 by root, Wed Apr 15 17:49:27 2009 UTC

…		…
2		2
3	libev - a high performance full-featured event loop written in C	3	libev - a high performance full-featured event loop written in C
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	#include <ev.h>	7	#include <ev.h>
8		8
9	=head1 EXAMPLE PROGRAM	9	=head2 EXAMPLE PROGRAM
10		10
		11	// a single header file is required
11	#include <ev.h>	12	#include <ev.h>
12		13
		14	#include <stdio.h> // for puts
		15
		16	// every watcher type has its own typedef'd struct
		17	// with the name ev_TYPE
13	ev_io stdin_watcher;	18	ev_io stdin_watcher;
14	ev_timer timeout_watcher;	19	ev_timer timeout_watcher;
15		20
16	/* called when data readable on stdin */	21	// all watcher callbacks have a similar signature
		22	// this callback is called when data is readable on stdin
17	static void	23	static void
18	stdin_cb (EV_P_ struct ev_io *w, int revents)	24	stdin_cb (EV_P_ ev_io *w, int revents)
19	{	25	{
20	/* puts ("stdin ready"); */	26	puts ("stdin ready");
21	ev_io_stop (EV_A_ w); /* just a syntax example */	27	// for one-shot events, one must manually stop the watcher
22	ev_unloop (EV_A_ EVUNLOOP_ALL); /* leave all loop calls */	28	// with its corresponding stop function.
		29	ev_io_stop (EV_A_ w);
		30
		31	// this causes all nested ev_loop's to stop iterating
		32	ev_unloop (EV_A_ EVUNLOOP_ALL);
23	}	33	}
24		34
		35	// another callback, this time for a time-out
25	static void	36	static void
26	timeout_cb (EV_P_ struct ev_timer *w, int revents)	37	timeout_cb (EV_P_ ev_timer *w, int revents)
27	{	38	{
28	/* puts ("timeout"); */	39	puts ("timeout");
29	ev_unloop (EV_A_ EVUNLOOP_ONE); /* leave one loop call */	40	// this causes the innermost ev_loop to stop iterating
		41	ev_unloop (EV_A_ EVUNLOOP_ONE);
30	}	42	}
31		43
32	int	44	int
33	main (void)	45	main (void)
34	{	46	{
		47	// use the default event loop unless you have special needs
35	struct ev_loop *loop = ev_default_loop (0);	48	struct ev_loop *loop = ev_default_loop (0);
36		49
37	/* initialise an io watcher, then start it */	50	// initialise an io watcher, then start it
		51	// this one will watch for stdin to become readable
38	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);	52	ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ);
39	ev_io_start (loop, &stdin_watcher);	53	ev_io_start (loop, &stdin_watcher);
40		54
		55	// initialise a timer watcher, then start it
41	/* simple non-repeating 5.5 second timeout */	56	// simple non-repeating 5.5 second timeout
42	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);	57	ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.);
43	ev_timer_start (loop, &timeout_watcher);	58	ev_timer_start (loop, &timeout_watcher);
44		59
45	/* loop till timeout or data ready */	60	// now wait for events to arrive
46	ev_loop (loop, 0);	61	ev_loop (loop, 0);
47		62
		63	// unloop was called, so exit
48	return 0;	64	return 0;
49	}	65	}
50		66
51	=head1 DESCRIPTION	67	=head1 DESCRIPTION
52		68
53	The newest version of this document is also available as a html-formatted	69	The newest version of this document is also available as an html-formatted
54	web page you might find easier to navigate when reading it for the first	70	web page you might find easier to navigate when reading it for the first
55	time: L<http://cvs.schmorp.de/libev/ev.html>.	71	time: L<http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod>.
56		72
57	Libev is an event loop: you register interest in certain events (such as a	73	Libev is an event loop: you register interest in certain events (such as a
58	file descriptor being readable or a timeout occurring), and it will manage	74	file descriptor being readable or a timeout occurring), and it will manage
59	these event sources and provide your program with events.	75	these event sources and provide your program with events.
60		76
…		…
65	You register interest in certain events by registering so-called I<event	81	You register interest in certain events by registering so-called I<event
66	watchers>, which are relatively small C structures you initialise with the	82	watchers>, which are relatively small C structures you initialise with the
67	details of the event, and then hand it over to libev by I<starting> the	83	details of the event, and then hand it over to libev by I<starting> the
68	watcher.	84	watcher.
69		85
70	=head1 FEATURES	86	=head2 FEATURES
71		87
72	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the	88	Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
73	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms	89	BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
74	for file descriptor events (C<ev_io>), the Linux C<inotify> interface	90	for file descriptor events (C<ev_io>), the Linux C<inotify> interface
75	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers	91	(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
…		…
82		98
83	It also is quite fast (see this	99	It also is quite fast (see this
84	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent	100	L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
85	for example).	101	for example).
86		102
87	=head1 CONVENTIONS	103	=head2 CONVENTIONS
88		104
89	Libev is very configurable. In this manual the default configuration will	105	Libev is very configurable. In this manual the default (and most common)
90	be described, which supports multiple event loops. For more info about	106	configuration will be described, which supports multiple event loops. For
91	various configuration options please have a look at B<EMBED> section in	107	more info about various configuration options please have a look at
92	this manual. If libev was configured without support for multiple event	108	B<EMBED> section in this manual. If libev was configured without support
93	loops, then all functions taking an initial argument of name C<loop>	109	for multiple event loops, then all functions taking an initial argument of
94	(which is always of type C<struct ev_loop *>) will not have this argument.	110	name C<loop> (which is always of type C<ev_loop *>) will not have
		111	this argument.
95		112
96	=head1 TIME REPRESENTATION	113	=head2 TIME REPRESENTATION
97		114
98	Libev represents time as a single floating point number, representing the	115	Libev represents time as a single floating point number, representing the
99	(fractional) number of seconds since the (POSIX) epoch (somewhere near	116	(fractional) number of seconds since the (POSIX) epoch (somewhere near
100	the beginning of 1970, details are complicated, don't ask). This type is	117	the beginning of 1970, details are complicated, don't ask). This type is
101	called C<ev_tstamp>, which is what you should use too. It usually aliases	118	called C<ev_tstamp>, which is what you should use too. It usually aliases
102	to the C<double> type in C, and when you need to do any calculations on	119	to the C<double> type in C, and when you need to do any calculations on
103	it, you should treat it as some floatingpoint value. Unlike the name	120	it, you should treat it as some floating point value. Unlike the name
104	component C<stamp> might indicate, it is also used for time differences	121	component C<stamp> might indicate, it is also used for time differences
105	throughout libev.	122	throughout libev.
		123
		124	=head1 ERROR HANDLING
		125
		126	Libev knows three classes of errors: operating system errors, usage errors
		127	and internal errors (bugs).
		128
		129	When libev catches an operating system error it cannot handle (for example
		130	a system call indicating a condition libev cannot fix), it calls the callback
		131	set via C<ev_set_syserr_cb>, which is supposed to fix the problem or
		132	abort. The default is to print a diagnostic message and to call C<abort
		133	()>.
		134
		135	When libev detects a usage error such as a negative timer interval, then
		136	it will print a diagnostic message and abort (via the C<assert> mechanism,
		137	so C<NDEBUG> will disable this checking): these are programming errors in
		138	the libev caller and need to be fixed there.
		139
		140	Libev also has a few internal error-checking C<assert>ions, and also has
		141	extensive consistency checking code. These do not trigger under normal
		142	circumstances, as they indicate either a bug in libev or worse.
		143
106		144
107	=head1 GLOBAL FUNCTIONS	145	=head1 GLOBAL FUNCTIONS
108		146
109	These functions can be called anytime, even before initialising the	147	These functions can be called anytime, even before initialising the
110	library in any way.	148	library in any way.
…		…
114	=item ev_tstamp ev_time ()	152	=item ev_tstamp ev_time ()
115		153
116	Returns the current time as libev would use it. Please note that the	154	Returns the current time as libev would use it. Please note that the
117	C<ev_now> function is usually faster and also often returns the timestamp	155	C<ev_now> function is usually faster and also often returns the timestamp
118	you actually want to know.	156	you actually want to know.
		157
		158	=item ev_sleep (ev_tstamp interval)
		159
		160	Sleep for the given interval: The current thread will be blocked until
		161	either it is interrupted or the given time interval has passed. Basically
		162	this is a sub-second-resolution C<sleep ()>.
119		163
120	=item int ev_version_major ()	164	=item int ev_version_major ()
121		165
122	=item int ev_version_minor ()	166	=item int ev_version_minor ()
123		167
…		…
136	not a problem.	180	not a problem.
137		181
138	Example: Make sure we haven't accidentally been linked against the wrong	182	Example: Make sure we haven't accidentally been linked against the wrong
139	version.	183	version.
140		184
141	assert (("libev version mismatch",	185	assert (("libev version mismatch",
142	ev_version_major () == EV_VERSION_MAJOR	186	ev_version_major () == EV_VERSION_MAJOR
143	&& ev_version_minor () >= EV_VERSION_MINOR));	187	&& ev_version_minor () >= EV_VERSION_MINOR));
144		188
145	=item unsigned int ev_supported_backends ()	189	=item unsigned int ev_supported_backends ()
146		190
147	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>	191	Return the set of all backends (i.e. their corresponding C<EV_BACKEND_*>
148	value) compiled into this binary of libev (independent of their	192	value) compiled into this binary of libev (independent of their
…		…
150	a description of the set values.	194	a description of the set values.
151		195
152	Example: make sure we have the epoll method, because yeah this is cool and	196	Example: make sure we have the epoll method, because yeah this is cool and
153	a must have and can we have a torrent of it please!!!11	197	a must have and can we have a torrent of it please!!!11
154		198
155	assert (("sorry, no epoll, no sex",	199	assert (("sorry, no epoll, no sex",
156	ev_supported_backends () & EVBACKEND_EPOLL));	200	ev_supported_backends () & EVBACKEND_EPOLL));
157		201
158	=item unsigned int ev_recommended_backends ()	202	=item unsigned int ev_recommended_backends ()
159		203
160	Return the set of all backends compiled into this binary of libev and also	204	Return the set of all backends compiled into this binary of libev and also
161	recommended for this platform. This set is often smaller than the one	205	recommended for this platform. This set is often smaller than the one
162	returned by C<ev_supported_backends>, as for example kqueue is broken on	206	returned by C<ev_supported_backends>, as for example kqueue is broken on
163	most BSDs and will not be autodetected unless you explicitly request it	207	most BSDs and will not be auto-detected unless you explicitly request it
164	(assuming you know what you are doing). This is the set of backends that	208	(assuming you know what you are doing). This is the set of backends that
165	libev will probe for if you specify no backends explicitly.	209	libev will probe for if you specify no backends explicitly.
166		210
167	=item unsigned int ev_embeddable_backends ()	211	=item unsigned int ev_embeddable_backends ()
168		212
…		…
172	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for	216	C<ev_embeddable_backends () & ev_supported_backends ()>, likewise for
173	recommended ones.	217	recommended ones.
174		218
175	See the description of C<ev_embed> watchers for more info.	219	See the description of C<ev_embed> watchers for more info.
176		220
177	=item ev_set_allocator (void *(*cb)(void *ptr, long size))	221	=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT]
178		222
179	Sets the allocation function to use (the prototype is similar - the	223	Sets the allocation function to use (the prototype is similar - the
180	semantics is identical - to the realloc C function). It is used to	224	semantics are identical to the C<realloc> C89/SuS/POSIX function). It is
181	allocate and free memory (no surprises here). If it returns zero when	225	used to allocate and free memory (no surprises here). If it returns zero
182	memory needs to be allocated, the library might abort or take some	226	when memory needs to be allocated (C<size != 0>), the library might abort
183	potentially destructive action. The default is your system realloc	227	or take some potentially destructive action.
184	function.	228
		229	Since some systems (at least OpenBSD and Darwin) fail to implement
		230	correct C<realloc> semantics, libev will use a wrapper around the system
		231	C<realloc> and C<free> functions by default.
185		232
186	You could override this function in high-availability programs to, say,	233	You could override this function in high-availability programs to, say,
187	free some memory if it cannot allocate memory, to use a special allocator,	234	free some memory if it cannot allocate memory, to use a special allocator,
188	or even to sleep a while and retry until some memory is available.	235	or even to sleep a while and retry until some memory is available.
189		236
190	Example: Replace the libev allocator with one that waits a bit and then	237	Example: Replace the libev allocator with one that waits a bit and then
191	retries).	238	retries (example requires a standards-compliant C<realloc>).
192		239
193	static void *	240	static void *
194	persistent_realloc (void *ptr, size_t size)	241	persistent_realloc (void *ptr, size_t size)
195	{	242	{
196	for (;;)	243	for (;;)
…		…
205	}	252	}
206		253
207	...	254	...
208	ev_set_allocator (persistent_realloc);	255	ev_set_allocator (persistent_realloc);
209		256
210	=item ev_set_syserr_cb (void (*cb)(const char *msg));	257	=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT]
211		258
212	Set the callback function to call on a retryable syscall error (such	259	Set the callback function to call on a retryable system call error (such
213	as failed select, poll, epoll_wait). The message is a printable string	260	as failed select, poll, epoll_wait). The message is a printable string
214	indicating the system call or subsystem causing the problem. If this	261	indicating the system call or subsystem causing the problem. If this
215	callback is set, then libev will expect it to remedy the sitution, no	262	callback is set, then libev will expect it to remedy the situation, no
216	matter what, when it returns. That is, libev will generally retry the	263	matter what, when it returns. That is, libev will generally retry the
217	requested operation, or, if the condition doesn't go away, do bad stuff	264	requested operation, or, if the condition doesn't go away, do bad stuff
218	(such as abort).	265	(such as abort).
219		266
220	Example: This is basically the same thing that libev does internally, too.	267	Example: This is basically the same thing that libev does internally, too.
…		…
231		278
232	=back	279	=back
233		280
234	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP	281	=head1 FUNCTIONS CONTROLLING THE EVENT LOOP
235		282
236	An event loop is described by a C<struct ev_loop *>. The library knows two	283	An event loop is described by a C<struct ev_loop *> (the C<struct>
237	types of such loops, the I<default> loop, which supports signals and child	284	is I<not> optional in this case, as there is also an C<ev_loop>
238	events, and dynamically created loops which do not.	285	I<function>).
239		286
240	If you use threads, a common model is to run the default event loop	287	The library knows two types of such loops, the I<default> loop, which
241	in your main thread (or in a separate thread) and for each thread you	288	supports signals and child events, and dynamically created loops which do
242	create, you also create another event loop. Libev itself does no locking	289	not.
243	whatsoever, so if you mix calls to the same event loop in different
244	threads, make sure you lock (this is usually a bad idea, though, even if
245	done correctly, because it's hideous and inefficient).
246		290
247	=over 4	291	=over 4
248		292
249	=item struct ev_loop *ev_default_loop (unsigned int flags)	293	=item struct ev_loop *ev_default_loop (unsigned int flags)
250		294
…		…
254	flags. If that is troubling you, check C<ev_backend ()> afterwards).	298	flags. If that is troubling you, check C<ev_backend ()> afterwards).
255		299
256	If you don't know what event loop to use, use the one returned from this	300	If you don't know what event loop to use, use the one returned from this
257	function.	301	function.
258		302
		303	Note that this function is I<not> thread-safe, so if you want to use it
		304	from multiple threads, you have to lock (note also that this is unlikely,
		305	as loops cannot be shared easily between threads anyway).
		306
		307	The default loop is the only loop that can handle C<ev_signal> and
		308	C<ev_child> watchers, and to do this, it always registers a handler
		309	for C<SIGCHLD>. If this is a problem for your application you can either
		310	create a dynamic loop with C<ev_loop_new> that doesn't do that, or you
		311	can simply overwrite the C<SIGCHLD> signal handler I<after> calling
		312	C<ev_default_init>.
		313
259	The flags argument can be used to specify special behaviour or specific	314	The flags argument can be used to specify special behaviour or specific
260	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).	315	backends to use, and is usually specified as C<0> (or C<EVFLAG_AUTO>).
261		316
262	The following flags are supported:	317	The following flags are supported:
263		318
…		…
268	The default flags value. Use this if you have no clue (it's the right	323	The default flags value. Use this if you have no clue (it's the right
269	thing, believe me).	324	thing, believe me).
270		325
271	=item C<EVFLAG_NOENV>	326	=item C<EVFLAG_NOENV>
272		327
273	If this flag bit is ored into the flag value (or the program runs setuid	328	If this flag bit is or'ed into the flag value (or the program runs setuid
274	or setgid) then libev will I<not> look at the environment variable	329	or setgid) then libev will I<not> look at the environment variable
275	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will	330	C<LIBEV_FLAGS>. Otherwise (the default), this environment variable will
276	override the flags completely if it is found in the environment. This is	331	override the flags completely if it is found in the environment. This is
277	useful to try out specific backends to test their performance, or to work	332	useful to try out specific backends to test their performance, or to work
278	around bugs.	333	around bugs.
…		…
284	enabling this flag.	339	enabling this flag.
285		340
286	This works by calling C<getpid ()> on every iteration of the loop,	341	This works by calling C<getpid ()> on every iteration of the loop,
287	and thus this might slow down your event loop if you do a lot of loop	342	and thus this might slow down your event loop if you do a lot of loop
288	iterations and little real work, but is usually not noticeable (on my	343	iterations and little real work, but is usually not noticeable (on my
289	Linux system for example, C<getpid> is actually a simple 5-insn sequence	344	GNU/Linux system for example, C<getpid> is actually a simple 5-insn sequence
290	without a syscall and thus I<very> fast, but my Linux system also has	345	without a system call and thus I<very> fast, but my GNU/Linux system also has
291	C<pthread_atfork> which is even faster).	346	C<pthread_atfork> which is even faster).
292		347
293	The big advantage of this flag is that you can forget about fork (and	348	The big advantage of this flag is that you can forget about fork (and
294	forget about forgetting to tell libev about forking) when you use this	349	forget about forgetting to tell libev about forking) when you use this
295	flag.	350	flag.
296		351
297	This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>	352	This flag setting cannot be overridden or specified in the C<LIBEV_FLAGS>
298	environment variable.	353	environment variable.
299		354
300	=item C<EVBACKEND_SELECT> (value 1, portable select backend)	355	=item C<EVBACKEND_SELECT> (value 1, portable select backend)
301		356
302	This is your standard select(2) backend. Not I<completely> standard, as	357	This is your standard select(2) backend. Not I<completely> standard, as
303	libev tries to roll its own fd_set with no limits on the number of fds,	358	libev tries to roll its own fd_set with no limits on the number of fds,
304	but if that fails, expect a fairly low limit on the number of fds when	359	but if that fails, expect a fairly low limit on the number of fds when
305	using this backend. It doesn't scale too well (O(highest_fd)), but its usually	360	using this backend. It doesn't scale too well (O(highest_fd)), but its
306	the fastest backend for a low number of fds.	361	usually the fastest backend for a low number of (low-numbered :) fds.
		362
		363	To get good performance out of this backend you need a high amount of
		364	parallelism (most of the file descriptors should be busy). If you are
		365	writing a server, you should C<accept ()> in a loop to accept as many
		366	connections as possible during one iteration. You might also want to have
		367	a look at C<ev_set_io_collect_interval ()> to increase the amount of
		368	readiness notifications you get per iteration.
		369
		370	This backend maps C<EV_READ> to the C<readfds> set and C<EV_WRITE> to the
		371	C<writefds> set (and to work around Microsoft Windows bugs, also onto the
		372	C<exceptfds> set on that platform).
307		373
308	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)	374	=item C<EVBACKEND_POLL> (value 2, poll backend, available everywhere except on windows)
309		375
310	And this is your standard poll(2) backend. It's more complicated than	376	And this is your standard poll(2) backend. It's more complicated
311	select, but handles sparse fds better and has no artificial limit on the	377	than select, but handles sparse fds better and has no artificial
312	number of fds you can use (except it will slow down considerably with a	378	limit on the number of fds you can use (except it will slow down
313	lot of inactive fds). It scales similarly to select, i.e. O(total_fds).	379	considerably with a lot of inactive fds). It scales similarly to select,
		380	i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
		381	performance tips.
		382
		383	This backend maps C<EV_READ> to C<POLLIN | POLLERR | POLLHUP>, and
		384	C<EV_WRITE> to C<POLLOUT | POLLERR | POLLHUP>.
314		385
315	=item C<EVBACKEND_EPOLL> (value 4, Linux)	386	=item C<EVBACKEND_EPOLL> (value 4, Linux)
316		387
317	For few fds, this backend is a bit little slower than poll and select,	388	For few fds, this backend is a bit little slower than poll and select,
318	but it scales phenomenally better. While poll and select usually scale	389	but it scales phenomenally better. While poll and select usually scale
319	like O(total_fds) where n is the total number of fds (or the highest fd),	390	like O(total_fds) where n is the total number of fds (or the highest fd),
320	epoll scales either O(1) or O(active_fds). The epoll design has a number	391	epoll scales either O(1) or O(active_fds).
321	of shortcomings, such as silently dropping events in some hard-to-detect	392
322	cases and rewuiring a syscall per fd change, no fork support and bad	393	The epoll mechanism deserves honorable mention as the most misdesigned
323	support for dup:	394	of the more advanced event mechanisms: mere annoyances include silently
		395	dropping file descriptors, requiring a system call per change per file
		396	descriptor (and unnecessary guessing of parameters), problems with dup and
		397	so on. The biggest issue is fork races, however - if a program forks then
		398	I<both> parent and child process have to recreate the epoll set, which can
		399	take considerable time (one syscall per file descriptor) and is of course
		400	hard to detect.
		401
		402	Epoll is also notoriously buggy - embedding epoll fds I<should> work, but
		403	of course I<doesn't>, and epoll just loves to report events for totally
		404	I<different> file descriptors (even already closed ones, so one cannot
		405	even remove them from the set) than registered in the set (especially
		406	on SMP systems). Libev tries to counter these spurious notifications by
		407	employing an additional generation counter and comparing that against the
		408	events to filter out spurious ones, recreating the set when required.
324		409
325	While stopping, setting and starting an I/O watcher in the same iteration	410	While stopping, setting and starting an I/O watcher in the same iteration
326	will result in some caching, there is still a syscall per such incident	411	will result in some caching, there is still a system call per such
327	(because the fd could point to a different file description now), so its	412	incident (because the same I<file descriptor> could point to a different
328	best to avoid that. Also, C<dup ()>'ed file descriptors might not work	413	I<file description> now), so its best to avoid that. Also, C<dup ()>'ed
329	very well if you register events for both fds.	414	file descriptors might not work very well if you register events for both
		415	file descriptors.
330		416
331	Please note that epoll sometimes generates spurious notifications, so you	417	Best performance from this backend is achieved by not unregistering all
332	need to use non-blocking I/O or other means to avoid blocking when no data	418	watchers for a file descriptor until it has been closed, if possible,
333	(or space) is available.	419	i.e. keep at least one watcher active per fd at all times. Stopping and
		420	starting a watcher (without re-setting it) also usually doesn't cause
		421	extra overhead. A fork can both result in spurious notifications as well
		422	as in libev having to destroy and recreate the epoll object, which can
		423	take considerable time and thus should be avoided.
		424
		425	All this means that, in practice, C<EVBACKEND_SELECT> can be as fast or
		426	faster than epoll for maybe up to a hundred file descriptors, depending on
		427	the usage. So sad.
		428
		429	While nominally embeddable in other event loops, this feature is broken in
		430	all kernel versions tested so far.
		431
		432	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		433	C<EVBACKEND_POLL>.
334		434
335	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)	435	=item C<EVBACKEND_KQUEUE> (value 8, most BSD clones)
336		436
337	Kqueue deserves special mention, as at the time of this writing, it	437	Kqueue deserves special mention, as at the time of this writing, it
338	was broken on I<all> BSDs (usually it doesn't work with anything but	438	was broken on all BSDs except NetBSD (usually it doesn't work reliably
339	sockets and pipes, except on Darwin, where of course it's completely	439	with anything but sockets and pipes, except on Darwin, where of course
340	useless. On NetBSD, it seems to work for all the FD types I tested, so it	440	it's completely useless). Unlike epoll, however, whose brokenness
341	is used by default there). For this reason it's not being "autodetected"	441	is by design, these kqueue bugs can (and eventually will) be fixed
		442	without API changes to existing programs. For this reason it's not being
342	unless you explicitly specify it explicitly in the flags (i.e. using	443	"auto-detected" unless you explicitly specify it in the flags (i.e. using
343	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)	444	C<EVBACKEND_KQUEUE>) or libev was compiled on a known-to-be-good (-enough)
344	system like NetBSD.	445	system like NetBSD.
345		446
		447	You still can embed kqueue into a normal poll or select backend and use it
		448	only for sockets (after having made sure that sockets work with kqueue on
		449	the target platform). See C<ev_embed> watchers for more info.
		450
346	It scales in the same way as the epoll backend, but the interface to the	451	It scales in the same way as the epoll backend, but the interface to the
347	kernel is more efficient (which says nothing about its actual speed,	452	kernel is more efficient (which says nothing about its actual speed, of
348	of course). While stopping, setting and starting an I/O watcher does	453	course). While stopping, setting and starting an I/O watcher does never
349	never cause an extra syscall as with epoll, it still adds up to two event	454	cause an extra system call as with C<EVBACKEND_EPOLL>, it still adds up to
350	changes per incident, support for C<fork ()> is very bad and it drops fds	455	two event changes per incident. Support for C<fork ()> is very bad (but
351	silently in similarly hard-to-detetc cases.	456	sane, unlike epoll) and it drops fds silently in similarly hard-to-detect
		457	cases
		458
		459	This backend usually performs well under most conditions.
		460
		461	While nominally embeddable in other event loops, this doesn't work
		462	everywhere, so you might need to test for this. And since it is broken
		463	almost everywhere, you should only use it when you have a lot of sockets
		464	(for which it usually works), by embedding it into another event loop
		465	(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> (but C<poll> is of course
		466	also broken on OS X)) and, did I mention it, using it only for sockets.
		467
		468	This backend maps C<EV_READ> into an C<EVFILT_READ> kevent with
		469	C<NOTE_EOF>, and C<EV_WRITE> into an C<EVFILT_WRITE> kevent with
		470	C<NOTE_EOF>.
352		471
353	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)	472	=item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
354		473
355	This is not implemented yet (and might never be).	474	This is not implemented yet (and might never be, unless you send me an
		475	implementation). According to reports, C</dev/poll> only supports sockets
		476	and is not embeddable, which would limit the usefulness of this backend
		477	immensely.
356		478
357	=item C<EVBACKEND_PORT> (value 32, Solaris 10)	479	=item C<EVBACKEND_PORT> (value 32, Solaris 10)
358		480
359	This uses the Solaris 10 event port mechanism. As with everything on Solaris,	481	This uses the Solaris 10 event port mechanism. As with everything on Solaris,
360	it's really slow, but it still scales very well (O(active_fds)).	482	it's really slow, but it still scales very well (O(active_fds)).
361		483
362	Please note that solaris event ports can deliver a lot of spurious	484	Please note that Solaris event ports can deliver a lot of spurious
363	notifications, so you need to use non-blocking I/O or other means to avoid	485	notifications, so you need to use non-blocking I/O or other means to avoid
364	blocking when no data (or space) is available.	486	blocking when no data (or space) is available.
		487
		488	While this backend scales well, it requires one system call per active
		489	file descriptor per loop iteration. For small and medium numbers of file
		490	descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
		491	might perform better.
		492
		493	On the positive side, with the exception of the spurious readiness
		494	notifications, this backend actually performed fully to specification
		495	in all tests and is fully embeddable, which is a rare feat among the
		496	OS-specific backends (I vastly prefer correctness over speed hacks).
		497
		498	This backend maps C<EV_READ> and C<EV_WRITE> in the same way as
		499	C<EVBACKEND_POLL>.
365		500
366	=item C<EVBACKEND_ALL>	501	=item C<EVBACKEND_ALL>
367		502
368	Try all backends (even potentially broken ones that wouldn't be tried	503	Try all backends (even potentially broken ones that wouldn't be tried
369	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as	504	with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
370	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.	505	C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
371		506
		507	It is definitely not recommended to use this flag.
		508
372	=back	509	=back
373		510
374	If one or more of these are ored into the flags value, then only these	511	If one or more of these are or'ed into the flags value, then only these
375	backends will be tried (in the reverse order as given here). If none are	512	backends will be tried (in the reverse order as listed here). If none are
376	specified, most compiled-in backend will be tried, usually in reverse	513	specified, all backends in C<ev_recommended_backends ()> will be tried.
377	order of their flag values :)
378		514
379	The most typical usage is like this:	515	Example: This is the most typical usage.
380		516
381	if (!ev_default_loop (0))	517	if (!ev_default_loop (0))
382	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");	518	fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?");
383		519
384	Restrict libev to the select and poll backends, and do not allow	520	Example: Restrict libev to the select and poll backends, and do not allow
385	environment settings to be taken into account:	521	environment settings to be taken into account:
386		522
387	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);	523	ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV);
388		524
389	Use whatever libev has to offer, but make sure that kqueue is used if	525	Example: Use whatever libev has to offer, but make sure that kqueue is
390	available (warning, breaks stuff, best use only with your own private	526	used if available (warning, breaks stuff, best use only with your own
391	event loop and only if you know the OS supports your types of fds):	527	private event loop and only if you know the OS supports your types of
		528	fds):
392		529
393	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);	530	ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE);
394		531
395	=item struct ev_loop *ev_loop_new (unsigned int flags)	532	=item struct ev_loop *ev_loop_new (unsigned int flags)
396		533
397	Similar to C<ev_default_loop>, but always creates a new event loop that is	534	Similar to C<ev_default_loop>, but always creates a new event loop that is
398	always distinct from the default loop. Unlike the default loop, it cannot	535	always distinct from the default loop. Unlike the default loop, it cannot
399	handle signal and child watchers, and attempts to do so will be greeted by	536	handle signal and child watchers, and attempts to do so will be greeted by
400	undefined behaviour (or a failed assertion if assertions are enabled).	537	undefined behaviour (or a failed assertion if assertions are enabled).
401		538
		539	Note that this function I<is> thread-safe, and the recommended way to use
		540	libev with threads is indeed to create one loop per thread, and using the
		541	default loop in the "main" or "initial" thread.
		542
402	Example: Try to create a event loop that uses epoll and nothing else.	543	Example: Try to create a event loop that uses epoll and nothing else.
403		544
404	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);	545	struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV);
405	if (!epoller)	546	if (!epoller)
406	fatal ("no epoll found here, maybe it hides under your chair");	547	fatal ("no epoll found here, maybe it hides under your chair");
407		548
408	=item ev_default_destroy ()	549	=item ev_default_destroy ()
409		550
410	Destroys the default loop again (frees all memory and kernel state	551	Destroys the default loop again (frees all memory and kernel state
411	etc.). None of the active event watchers will be stopped in the normal	552	etc.). None of the active event watchers will be stopped in the normal
412	sense, so e.g. C<ev_is_active> might still return true. It is your	553	sense, so e.g. C<ev_is_active> might still return true. It is your
413	responsibility to either stop all watchers cleanly yoursef I<before>	554	responsibility to either stop all watchers cleanly yourself I<before>
414	calling this function, or cope with the fact afterwards (which is usually	555	calling this function, or cope with the fact afterwards (which is usually
415	the easiest thing, you can just ignore the watchers and/or C<free ()> them	556	the easiest thing, you can just ignore the watchers and/or C<free ()> them
416	for example).	557	for example).
417		558
418	Note that certain global state, such as signal state, will not be freed by	559	Note that certain global state, such as signal state (and installed signal
419	this function, and related watchers (such as signal and child watchers)	560	handlers), will not be freed by this function, and related watchers (such
420	would need to be stopped manually.	561	as signal and child watchers) would need to be stopped manually.
421		562
422	In general it is not advisable to call this function except in the	563	In general it is not advisable to call this function except in the
423	rare occasion where you really need to free e.g. the signal handling	564	rare occasion where you really need to free e.g. the signal handling
424	pipe fds. If you need dynamically allocated loops it is better to use	565	pipe fds. If you need dynamically allocated loops it is better to use
425	C<ev_loop_new> and C<ev_loop_destroy>).	566	C<ev_loop_new> and C<ev_loop_destroy>).
…		…
429	Like C<ev_default_destroy>, but destroys an event loop created by an	570	Like C<ev_default_destroy>, but destroys an event loop created by an
430	earlier call to C<ev_loop_new>.	571	earlier call to C<ev_loop_new>.
431		572
432	=item ev_default_fork ()	573	=item ev_default_fork ()
433		574
		575	This function sets a flag that causes subsequent C<ev_loop> iterations
434	This function reinitialises the kernel state for backends that have	576	to reinitialise the kernel state for backends that have one. Despite the
435	one. Despite the name, you can call it anytime, but it makes most sense	577	name, you can call it anytime, but it makes most sense after forking, in
436	after forking, in either the parent or child process (or both, but that	578	the child process (or both child and parent, but that again makes little
437	again makes little sense).	579	sense). You I<must> call it in the child before using any of the libev
		580	functions, and it will only take effect at the next C<ev_loop> iteration.
438		581
439	You I<must> call this function in the child process after forking if and	582	On the other hand, you only need to call this function in the child
440	only if you want to use the event library in both processes. If you just	583	process if and only if you want to use the event library in the child. If
441	fork+exec, you don't have to call it.	584	you just fork+exec, you don't have to call it at all.
442		585
443	The function itself is quite fast and it's usually not a problem to call	586	The function itself is quite fast and it's usually not a problem to call
444	it just in case after a fork. To make this easy, the function will fit in	587	it just in case after a fork. To make this easy, the function will fit in
445	quite nicely into a call to C<pthread_atfork>:	588	quite nicely into a call to C<pthread_atfork>:
446		589
447	pthread_atfork (0, 0, ev_default_fork);	590	pthread_atfork (0, 0, ev_default_fork);
448		591
449	At the moment, C<EVBACKEND_SELECT> and C<EVBACKEND_POLL> are safe to use
450	without calling this function, so if you force one of those backends you
451	do not need to care.
452
453	=item ev_loop_fork (loop)	592	=item ev_loop_fork (loop)
454		593
455	Like C<ev_default_fork>, but acts on an event loop created by	594	Like C<ev_default_fork>, but acts on an event loop created by
456	C<ev_loop_new>. Yes, you have to call this on every allocated event loop	595	C<ev_loop_new>. Yes, you have to call this on every allocated event loop
457	after fork, and how you do this is entirely your own problem.	596	after fork that you want to re-use in the child, and how you do this is
		597	entirely your own problem.
		598
		599	=item int ev_is_default_loop (loop)
		600
		601	Returns true when the given loop is, in fact, the default loop, and false
		602	otherwise.
458		603
459	=item unsigned int ev_loop_count (loop)	604	=item unsigned int ev_loop_count (loop)
460		605
461	Returns the count of loop iterations for the loop, which is identical to	606	Returns the count of loop iterations for the loop, which is identical to
462	the number of times libev did poll for new events. It starts at C<0> and	607	the number of times libev did poll for new events. It starts at C<0> and
…		…
477	received events and started processing them. This timestamp does not	622	received events and started processing them. This timestamp does not
478	change as long as callbacks are being processed, and this is also the base	623	change as long as callbacks are being processed, and this is also the base
479	time used for relative timers. You can treat it as the timestamp of the	624	time used for relative timers. You can treat it as the timestamp of the
480	event occurring (or more correctly, libev finding out about it).	625	event occurring (or more correctly, libev finding out about it).
481		626
		627	=item ev_now_update (loop)
		628
		629	Establishes the current time by querying the kernel, updating the time
		630	returned by C<ev_now ()> in the progress. This is a costly operation and
		631	is usually done automatically within C<ev_loop ()>.
		632
		633	This function is rarely useful, but when some event callback runs for a
		634	very long time without entering the event loop, updating libev's idea of
		635	the current time is a good idea.
		636
		637	See also "The special problem of time updates" in the C<ev_timer> section.
		638
482	=item ev_loop (loop, int flags)	639	=item ev_loop (loop, int flags)
483		640
484	Finally, this is it, the event handler. This function usually is called	641	Finally, this is it, the event handler. This function usually is called
485	after you initialised all your watchers and you want to start handling	642	after you initialised all your watchers and you want to start handling
486	events.	643	events.
…		…
488	If the flags argument is specified as C<0>, it will not return until	645	If the flags argument is specified as C<0>, it will not return until
489	either no event watchers are active anymore or C<ev_unloop> was called.	646	either no event watchers are active anymore or C<ev_unloop> was called.
490		647
491	Please note that an explicit C<ev_unloop> is usually better than	648	Please note that an explicit C<ev_unloop> is usually better than
492	relying on all watchers to be stopped when deciding when a program has	649	relying on all watchers to be stopped when deciding when a program has
493	finished (especially in interactive programs), but having a program that	650	finished (especially in interactive programs), but having a program
494	automatically loops as long as it has to and no longer by virtue of	651	that automatically loops as long as it has to and no longer by virtue
495	relying on its watchers stopping correctly is a thing of beauty.	652	of relying on its watchers stopping correctly, that is truly a thing of
		653	beauty.
496		654
497	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle	655	A flags value of C<EVLOOP_NONBLOCK> will look for new events, will handle
498	those events and any outstanding ones, but will not block your process in	656	those events and any already outstanding ones, but will not block your
499	case there are no events and will return after one iteration of the loop.	657	process in case there are no events and will return after one iteration of
		658	the loop.
500		659
501	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if	660	A flags value of C<EVLOOP_ONESHOT> will look for new events (waiting if
502	neccessary) and will handle those and any outstanding ones. It will block	661	necessary) and will handle those and any already outstanding ones. It
503	your process until at least one new event arrives, and will return after	662	will block your process until at least one new event arrives (which could
504	one iteration of the loop. This is useful if you are waiting for some	663	be an event internal to libev itself, so there is no guarantee that a
505	external event in conjunction with something not expressible using other	664	user-registered callback will be called), and will return after one
		665	iteration of the loop.
		666
		667	This is useful if you are waiting for some external event in conjunction
		668	with something not expressible using other libev watchers (i.e. "roll your
506	libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is	669	own C<ev_loop>"). However, a pair of C<ev_prepare>/C<ev_check> watchers is
507	usually a better approach for this kind of thing.	670	usually a better approach for this kind of thing.
508		671
509	Here are the gory details of what C<ev_loop> does:	672	Here are the gory details of what C<ev_loop> does:
510		673
511	- Before the first iteration, call any pending watchers.	674	- Before the first iteration, call any pending watchers.
512	* If there are no active watchers (reference count is zero), return.	675	* If EVFLAG_FORKCHECK was used, check for a fork.
513	- Queue all prepare watchers and then call all outstanding watchers.	676	- If a fork was detected (by any means), queue and call all fork watchers.
		677	- Queue and call all prepare watchers.
514	- If we have been forked, recreate the kernel state.	678	- If we have been forked, detach and recreate the kernel state
		679	as to not disturb the other process.
515	- Update the kernel state with all outstanding changes.	680	- Update the kernel state with all outstanding changes.
516	- Update the "event loop time".	681	- Update the "event loop time" (ev_now ()).
517	- Calculate for how long to block.	682	- Calculate for how long to sleep or block, if at all
		683	(active idle watchers, EVLOOP_NONBLOCK or not having
		684	any active watchers at all will result in not sleeping).
		685	- Sleep if the I/O and timer collect interval say so.
518	- Block the process, waiting for any events.	686	- Block the process, waiting for any events.
519	- Queue all outstanding I/O (fd) events.	687	- Queue all outstanding I/O (fd) events.
520	- Update the "event loop time" and do time jump handling.	688	- Update the "event loop time" (ev_now ()), and do time jump adjustments.
521	- Queue all outstanding timers.	689	- Queue all expired timers.
522	- Queue all outstanding periodics.	690	- Queue all expired periodics.
523	- If no events are pending now, queue all idle watchers.	691	- Unless any events are pending now, queue all idle watchers.
524	- Queue all check watchers.	692	- Queue all check watchers.
525	- Call all queued watchers in reverse order (i.e. check watchers first).	693	- Call all queued watchers in reverse order (i.e. check watchers first).
526	Signals and child watchers are implemented as I/O watchers, and will	694	Signals and child watchers are implemented as I/O watchers, and will
527	be handled here by queueing them when their watcher gets executed.	695	be handled here by queueing them when their watcher gets executed.
528	- If ev_unloop has been called or EVLOOP_ONESHOT or EVLOOP_NONBLOCK	696	- If ev_unloop has been called, or EVLOOP_ONESHOT or EVLOOP_NONBLOCK
529	were used, return, otherwise continue with step *.	697	were used, or there are no active watchers, return, otherwise
		698	continue with step *.
530		699
531	Example: Queue some jobs and then loop until no events are outsanding	700	Example: Queue some jobs and then loop until no events are outstanding
532	anymore.	701	anymore.
533		702
534	... queue jobs here, make sure they register event watchers as long	703	... queue jobs here, make sure they register event watchers as long
535	... as they still have work to do (even an idle watcher will do..)	704	... as they still have work to do (even an idle watcher will do..)
536	ev_loop (my_loop, 0);	705	ev_loop (my_loop, 0);
537	... jobs done. yeah!	706	... jobs done or somebody called unloop. yeah!
538		707
539	=item ev_unloop (loop, how)	708	=item ev_unloop (loop, how)
540		709
541	Can be used to make a call to C<ev_loop> return early (but only after it	710	Can be used to make a call to C<ev_loop> return early (but only after it
542	has processed all outstanding events). The C<how> argument must be either	711	has processed all outstanding events). The C<how> argument must be either
543	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or	712	C<EVUNLOOP_ONE>, which will make the innermost C<ev_loop> call return, or
544	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.	713	C<EVUNLOOP_ALL>, which will make all nested C<ev_loop> calls return.
545		714
		715	This "unloop state" will be cleared when entering C<ev_loop> again.
		716
		717	It is safe to call C<ev_unloop> from otuside any C<ev_loop> calls.
		718
546	=item ev_ref (loop)	719	=item ev_ref (loop)
547		720
548	=item ev_unref (loop)	721	=item ev_unref (loop)
549		722
550	Ref/unref can be used to add or remove a reference count on the event	723	Ref/unref can be used to add or remove a reference count on the event
551	loop: Every watcher keeps one reference, and as long as the reference	724	loop: Every watcher keeps one reference, and as long as the reference
552	count is nonzero, C<ev_loop> will not return on its own. If you have	725	count is nonzero, C<ev_loop> will not return on its own.
		726
553	a watcher you never unregister that should not keep C<ev_loop> from	727	If you have a watcher you never unregister that should not keep C<ev_loop>
554	returning, ev_unref() after starting, and ev_ref() before stopping it. For	728	from returning, call ev_unref() after starting, and ev_ref() before
		729	stopping it.
		730
555	example, libev itself uses this for its internal signal pipe: It is not	731	As an example, libev itself uses this for its internal signal pipe: It
556	visible to the libev user and should not keep C<ev_loop> from exiting if	732	is not visible to the libev user and should not keep C<ev_loop> from
557	no event watchers registered by it are active. It is also an excellent	733	exiting if no event watchers registered by it are active. It is also an
558	way to do this for generic recurring timers or from within third-party	734	excellent way to do this for generic recurring timers or from within
559	libraries. Just remember to I<unref after start> and I<ref before stop>.	735	third-party libraries. Just remember to I<unref after start> and I<ref
		736	before stop> (but only if the watcher wasn't active before, or was active
		737	before, respectively. Note also that libev might stop watchers itself
		738	(e.g. non-repeating timers) in which case you have to C<ev_ref>
		739	in the callback).
560		740
561	Example: Create a signal watcher, but keep it from keeping C<ev_loop>	741	Example: Create a signal watcher, but keep it from keeping C<ev_loop>
562	running when nothing else is active.	742	running when nothing else is active.
563		743
564	struct ev_signal exitsig;	744	ev_signal exitsig;
565	ev_signal_init (&exitsig, sig_cb, SIGINT);	745	ev_signal_init (&exitsig, sig_cb, SIGINT);
566	ev_signal_start (loop, &exitsig);	746	ev_signal_start (loop, &exitsig);
567	evf_unref (loop);	747	evf_unref (loop);
568		748
569	Example: For some weird reason, unregister the above signal handler again.	749	Example: For some weird reason, unregister the above signal handler again.
570		750
571	ev_ref (loop);	751	ev_ref (loop);
572	ev_signal_stop (loop, &exitsig);	752	ev_signal_stop (loop, &exitsig);
		753
		754	=item ev_set_io_collect_interval (loop, ev_tstamp interval)
		755
		756	=item ev_set_timeout_collect_interval (loop, ev_tstamp interval)
		757
		758	These advanced functions influence the time that libev will spend waiting
		759	for events. Both time intervals are by default C<0>, meaning that libev
		760	will try to invoke timer/periodic callbacks and I/O callbacks with minimum
		761	latency.
		762
		763	Setting these to a higher value (the C<interval> I<must> be >= C<0>)
		764	allows libev to delay invocation of I/O and timer/periodic callbacks
		765	to increase efficiency of loop iterations (or to increase power-saving
		766	opportunities).
		767
		768	The idea is that sometimes your program runs just fast enough to handle
		769	one (or very few) event(s) per loop iteration. While this makes the
		770	program responsive, it also wastes a lot of CPU time to poll for new
		771	events, especially with backends like C<select ()> which have a high
		772	overhead for the actual polling but can deliver many events at once.
		773
		774	By setting a higher I<io collect interval> you allow libev to spend more
		775	time collecting I/O events, so you can handle more events per iteration,
		776	at the cost of increasing latency. Timeouts (both C<ev_periodic> and
		777	C<ev_timer>) will be not affected. Setting this to a non-null value will
		778	introduce an additional C<ev_sleep ()> call into most loop iterations.
		779
		780	Likewise, by setting a higher I<timeout collect interval> you allow libev
		781	to spend more time collecting timeouts, at the expense of increased
		782	latency/jitter/inexactness (the watcher callback will be called
		783	later). C<ev_io> watchers will not be affected. Setting this to a non-null
		784	value will not introduce any overhead in libev.
		785
		786	Many (busy) programs can usually benefit by setting the I/O collect
		787	interval to a value near C<0.1> or so, which is often enough for
		788	interactive servers (of course not for games), likewise for timeouts. It
		789	usually doesn't make much sense to set it to a lower value than C<0.01>,
		790	as this approaches the timing granularity of most systems.
		791
		792	Setting the I<timeout collect interval> can improve the opportunity for
		793	saving power, as the program will "bundle" timer callback invocations that
		794	are "near" in time together, by delaying some, thus reducing the number of
		795	times the process sleeps and wakes up again. Another useful technique to
		796	reduce iterations/wake-ups is to use C<ev_periodic> watchers and make sure
		797	they fire on, say, one-second boundaries only.
		798
		799	=item ev_loop_verify (loop)
		800
		801	This function only does something when C<EV_VERIFY> support has been
		802	compiled in, which is the default for non-minimal builds. It tries to go
		803	through all internal structures and checks them for validity. If anything
		804	is found to be inconsistent, it will print an error message to standard
		805	error and call C<abort ()>.
		806
		807	This can be used to catch bugs inside libev itself: under normal
		808	circumstances, this function will never abort as of course libev keeps its
		809	data structures consistent.
573		810
574	=back	811	=back
575		812
576		813
577	=head1 ANATOMY OF A WATCHER	814	=head1 ANATOMY OF A WATCHER
		815
		816	In the following description, uppercase C<TYPE> in names stands for the
		817	watcher type, e.g. C<ev_TYPE_start> can mean C<ev_timer_start> for timer
		818	watchers and C<ev_io_start> for I/O watchers.
578		819
579	A watcher is a structure that you create and register to record your	820	A watcher is a structure that you create and register to record your
580	interest in some event. For instance, if you want to wait for STDIN to	821	interest in some event. For instance, if you want to wait for STDIN to
581	become readable, you would create an C<ev_io> watcher for that:	822	become readable, you would create an C<ev_io> watcher for that:
582		823
583	static void my_cb (struct ev_loop *loop, struct ev_io *w, int revents)	824	static void my_cb (struct ev_loop *loop, ev_io *w, int revents)
584	{	825	{
585	ev_io_stop (w);	826	ev_io_stop (w);
586	ev_unloop (loop, EVUNLOOP_ALL);	827	ev_unloop (loop, EVUNLOOP_ALL);
587	}	828	}
588		829
589	struct ev_loop *loop = ev_default_loop (0);	830	struct ev_loop *loop = ev_default_loop (0);
		831
590	struct ev_io stdin_watcher;	832	ev_io stdin_watcher;
		833
591	ev_init (&stdin_watcher, my_cb);	834	ev_init (&stdin_watcher, my_cb);
592	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);	835	ev_io_set (&stdin_watcher, STDIN_FILENO, EV_READ);
593	ev_io_start (loop, &stdin_watcher);	836	ev_io_start (loop, &stdin_watcher);
		837
594	ev_loop (loop, 0);	838	ev_loop (loop, 0);
595		839
596	As you can see, you are responsible for allocating the memory for your	840	As you can see, you are responsible for allocating the memory for your
597	watcher structures (and it is usually a bad idea to do this on the stack,	841	watcher structures (and it is I<usually> a bad idea to do this on the
598	although this can sometimes be quite valid).	842	stack).
		843
		844	Each watcher has an associated watcher structure (called C<struct ev_TYPE>
		845	or simply C<ev_TYPE>, as typedefs are provided for all watcher structs).
599		846
600	Each watcher structure must be initialised by a call to C<ev_init	847	Each watcher structure must be initialised by a call to C<ev_init
601	(watcher *, callback)>, which expects a callback to be provided. This	848	(watcher *, callback)>, which expects a callback to be provided. This
602	callback gets invoked each time the event occurs (or, in the case of io	849	callback gets invoked each time the event occurs (or, in the case of I/O
603	watchers, each time the event loop detects that the file descriptor given	850	watchers, each time the event loop detects that the file descriptor given
604	is readable and/or writable).	851	is readable and/or writable).
605		852
606	Each watcher type has its own C<< ev_<type>_set (watcher *, ...) >> macro	853	Each watcher type further has its own C<< ev_TYPE_set (watcher *, ...) >>
607	with arguments specific to this watcher type. There is also a macro	854	macro to configure it, with arguments specific to the watcher type. There
608	to combine initialisation and setting in one call: C<< ev_<type>_init	855	is also a macro to combine initialisation and setting in one call: C<<
609	(watcher *, callback, ...) >>.	856	ev_TYPE_init (watcher *, callback, ...) >>.
610		857
611	To make the watcher actually watch out for events, you have to start it	858	To make the watcher actually watch out for events, you have to start it
612	with a watcher-specific start function (C<< ev_<type>_start (loop, watcher	859	with a watcher-specific start function (C<< ev_TYPE_start (loop, watcher
613	*) >>), and you can stop watching for events at any time by calling the	860	*) >>), and you can stop watching for events at any time by calling the
614	corresponding stop function (C<< ev_<type>_stop (loop, watcher *) >>.	861	corresponding stop function (C<< ev_TYPE_stop (loop, watcher *) >>.
615		862
616	As long as your watcher is active (has been started but not stopped) you	863	As long as your watcher is active (has been started but not stopped) you
617	must not touch the values stored in it. Most specifically you must never	864	must not touch the values stored in it. Most specifically you must never
618	reinitialise it or call its C<set> macro.	865	reinitialise it or call its C<ev_TYPE_set> macro.
619		866
620	Each and every callback receives the event loop pointer as first, the	867	Each and every callback receives the event loop pointer as first, the
621	registered watcher structure as second, and a bitset of received events as	868	registered watcher structure as second, and a bitset of received events as
622	third argument.	869	third argument.
623		870
…		…
677	=item C<EV_FORK>	924	=item C<EV_FORK>
678		925
679	The event loop has been resumed in the child process after fork (see	926	The event loop has been resumed in the child process after fork (see
680	C<ev_fork>).	927	C<ev_fork>).
681		928
		929	=item C<EV_ASYNC>
		930
		931	The given async watcher has been asynchronously notified (see C<ev_async>).
		932
		933	=item C<EV_CUSTOM>
		934
		935	Not ever sent (or otherwise used) by libev itself, but can be freely used
		936	by libev users to signal watchers (e.g. via C<ev_feed_event>).
		937
682	=item C<EV_ERROR>	938	=item C<EV_ERROR>
683		939
684	An unspecified error has occured, the watcher has been stopped. This might	940	An unspecified error has occurred, the watcher has been stopped. This might
685	happen because the watcher could not be properly started because libev	941	happen because the watcher could not be properly started because libev
686	ran out of memory, a file descriptor was found to be closed or any other	942	ran out of memory, a file descriptor was found to be closed or any other
		943	problem. Libev considers these application bugs.
		944
687	problem. You best act on it by reporting the problem and somehow coping	945	You best act on it by reporting the problem and somehow coping with the
688	with the watcher being stopped.	946	watcher being stopped. Note that well-written programs should not receive
		947	an error ever, so when your watcher receives it, this usually indicates a
		948	bug in your program.
689		949
690	Libev will usually signal a few "dummy" events together with an error,	950	Libev will usually signal a few "dummy" events together with an error, for
691	for example it might indicate that a fd is readable or writable, and if	951	example it might indicate that a fd is readable or writable, and if your
692	your callbacks is well-written it can just attempt the operation and cope	952	callbacks is well-written it can just attempt the operation and cope with
693	with the error from read() or write(). This will not work in multithreaded	953	the error from read() or write(). This will not work in multi-threaded
694	programs, though, so beware.	954	programs, though, as the fd could already be closed and reused for another
		955	thing, so beware.
695		956
696	=back	957	=back
697		958
698	=head2 GENERIC WATCHER FUNCTIONS	959	=head2 GENERIC WATCHER FUNCTIONS
699
700	In the following description, C<TYPE> stands for the watcher type,
701	e.g. C<timer> for C<ev_timer> watchers and C<io> for C<ev_io> watchers.
702		960
703	=over 4	961	=over 4
704		962
705	=item C<ev_init> (ev_TYPE *watcher, callback)	963	=item C<ev_init> (ev_TYPE *watcher, callback)
706		964
…		…
712	which rolls both calls into one.	970	which rolls both calls into one.
713		971
714	You can reinitialise a watcher at any time as long as it has been stopped	972	You can reinitialise a watcher at any time as long as it has been stopped
715	(or never started) and there are no pending events outstanding.	973	(or never started) and there are no pending events outstanding.
716		974
717	The callback is always of type C<void (*)(ev_loop *loop, ev_TYPE *watcher,	975	The callback is always of type C<void (*)(struct ev_loop *loop, ev_TYPE *watcher,
718	int revents)>.	976	int revents)>.
		977
		978	Example: Initialise an C<ev_io> watcher in two steps.
		979
		980	ev_io w;
		981	ev_init (&w, my_cb);
		982	ev_io_set (&w, STDIN_FILENO, EV_READ);
719		983
720	=item C<ev_TYPE_set> (ev_TYPE *, [args])	984	=item C<ev_TYPE_set> (ev_TYPE *, [args])
721		985
722	This macro initialises the type-specific parts of a watcher. You need to	986	This macro initialises the type-specific parts of a watcher. You need to
723	call C<ev_init> at least once before you call this macro, but you can	987	call C<ev_init> at least once before you call this macro, but you can
…		…
726	difference to the C<ev_init> macro).	990	difference to the C<ev_init> macro).
727		991
728	Although some watcher types do not have type-specific arguments	992	Although some watcher types do not have type-specific arguments
729	(e.g. C<ev_prepare>) you still need to call its C<set> macro.	993	(e.g. C<ev_prepare>) you still need to call its C<set> macro.
730		994
		995	See C<ev_init>, above, for an example.
		996
731	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])	997	=item C<ev_TYPE_init> (ev_TYPE *watcher, callback, [args])
732		998
733	This convinience macro rolls both C<ev_init> and C<ev_TYPE_set> macro	999	This convenience macro rolls both C<ev_init> and C<ev_TYPE_set> macro
734	calls into a single call. This is the most convinient method to initialise	1000	calls into a single call. This is the most convenient method to initialise
735	a watcher. The same limitations apply, of course.	1001	a watcher. The same limitations apply, of course.
		1002
		1003	Example: Initialise and set an C<ev_io> watcher in one step.
		1004
		1005	ev_io_init (&w, my_cb, STDIN_FILENO, EV_READ);
736		1006
737	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)	1007	=item C<ev_TYPE_start> (loop *, ev_TYPE *watcher)
738		1008
739	Starts (activates) the given watcher. Only active watchers will receive	1009	Starts (activates) the given watcher. Only active watchers will receive
740	events. If the watcher is already active nothing will happen.	1010	events. If the watcher is already active nothing will happen.
741		1011
		1012	Example: Start the C<ev_io> watcher that is being abused as example in this
		1013	whole section.
		1014
		1015	ev_io_start (EV_DEFAULT_UC, &w);
		1016
742	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)	1017	=item C<ev_TYPE_stop> (loop *, ev_TYPE *watcher)
743		1018
744	Stops the given watcher again (if active) and clears the pending	1019	Stops the given watcher if active, and clears the pending status (whether
		1020	the watcher was active or not).
		1021
745	status. It is possible that stopped watchers are pending (for example,	1022	It is possible that stopped watchers are pending - for example,
746	non-repeating timers are being stopped when they become pending), but	1023	non-repeating timers are being stopped when they become pending - but
747	C<ev_TYPE_stop> ensures that the watcher is neither active nor pending. If	1024	calling C<ev_TYPE_stop> ensures that the watcher is neither active nor
748	you want to free or reuse the memory used by the watcher it is therefore a	1025	pending. If you want to free or reuse the memory used by the watcher it is
749	good idea to always call its C<ev_TYPE_stop> function.	1026	therefore a good idea to always call its C<ev_TYPE_stop> function.
750		1027
751	=item bool ev_is_active (ev_TYPE *watcher)	1028	=item bool ev_is_active (ev_TYPE *watcher)
752		1029
753	Returns a true value iff the watcher is active (i.e. it has been started	1030	Returns a true value iff the watcher is active (i.e. it has been started
754	and not yet been stopped). As long as a watcher is active you must not modify	1031	and not yet been stopped). As long as a watcher is active you must not modify
…		…
796	The default priority used by watchers when no priority has been set is	1073	The default priority used by watchers when no priority has been set is
797	always C<0>, which is supposed to not be too high and not be too low :).	1074	always C<0>, which is supposed to not be too high and not be too low :).
798		1075
799	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is	1076	Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
800	fine, as long as you do not mind that the priority value you query might	1077	fine, as long as you do not mind that the priority value you query might
801	or might not have been adjusted to be within valid range.	1078	or might not have been clamped to the valid range.
802		1079
803	=item ev_invoke (loop, ev_TYPE *watcher, int revents)	1080	=item ev_invoke (loop, ev_TYPE *watcher, int revents)
804		1081
805	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither	1082	Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
806	C<loop> nor C<revents> need to be valid as long as the watcher callback	1083	C<loop> nor C<revents> need to be valid as long as the watcher callback
807	can deal with that fact.	1084	can deal with that fact, as both are simply passed through to the
		1085	callback.
808		1086
809	=item int ev_clear_pending (loop, ev_TYPE *watcher)	1087	=item int ev_clear_pending (loop, ev_TYPE *watcher)
810		1088
811	If the watcher is pending, this function returns clears its pending status	1089	If the watcher is pending, this function clears its pending status and
812	and returns its C<revents> bitset (as if its callback was invoked). If the	1090	returns its C<revents> bitset (as if its callback was invoked). If the
813	watcher isn't pending it does nothing and returns C<0>.	1091	watcher isn't pending it does nothing and returns C<0>.
814		1092
		1093	Sometimes it can be useful to "poll" a watcher instead of waiting for its
		1094	callback to be invoked, which can be accomplished with this function.
		1095
815	=back	1096	=back
816		1097
817		1098
818	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER	1099	=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
819		1100
820	Each watcher has, by default, a member C<void *data> that you can change	1101	Each watcher has, by default, a member C<void *data> that you can change
821	and read at any time, libev will completely ignore it. This can be used	1102	and read at any time: libev will completely ignore it. This can be used
822	to associate arbitrary data with your watcher. If you need more data and	1103	to associate arbitrary data with your watcher. If you need more data and
823	don't want to allocate memory and store a pointer to it in that data	1104	don't want to allocate memory and store a pointer to it in that data
824	member, you can also "subclass" the watcher type and provide your own	1105	member, you can also "subclass" the watcher type and provide your own
825	data:	1106	data:
826		1107
827	struct my_io	1108	struct my_io
828	{	1109	{
829	struct ev_io io;	1110	ev_io io;
830	int otherfd;	1111	int otherfd;
831	void *somedata;	1112	void *somedata;
832	struct whatever *mostinteresting;	1113	struct whatever *mostinteresting;
833	}	1114	};
		1115
		1116	...
		1117	struct my_io w;
		1118	ev_io_init (&w.io, my_cb, fd, EV_READ);
834		1119
835	And since your callback will be called with a pointer to the watcher, you	1120	And since your callback will be called with a pointer to the watcher, you
836	can cast it back to your own type:	1121	can cast it back to your own type:
837		1122
838	static void my_cb (struct ev_loop *loop, struct ev_io *w_, int revents)	1123	static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)
839	{	1124	{
840	struct my_io *w = (struct my_io *)w_;	1125	struct my_io *w = (struct my_io *)w_;
841	...	1126	...
842	}	1127	}
843		1128
844	More interesting and less C-conformant ways of casting your callback type	1129	More interesting and less C-conformant ways of casting your callback type
845	instead have been omitted.	1130	instead have been omitted.
846		1131
847	Another common scenario is having some data structure with multiple	1132	Another common scenario is to use some data structure with multiple
848	watchers:	1133	embedded watchers:
849		1134
850	struct my_biggy	1135	struct my_biggy
851	{	1136	{
852	int some_data;	1137	int some_data;
853	ev_timer t1;	1138	ev_timer t1;
854	ev_timer t2;	1139	ev_timer t2;
855	}	1140	}
856		1141
857	In this case getting the pointer to C<my_biggy> is a bit more complicated,	1142	In this case getting the pointer to C<my_biggy> is a bit more
858	you need to use C<offsetof>:	1143	complicated: Either you store the address of your C<my_biggy> struct
		1144	in the C<data> member of the watcher (for woozies), or you need to use
		1145	some pointer arithmetic using C<offsetof> inside your watchers (for real
		1146	programmers):
859		1147
860	#include <stddef.h>	1148	#include <stddef.h>
861		1149
862	static void	1150	static void
863	t1_cb (EV_P_ struct ev_timer *w, int revents)	1151	t1_cb (EV_P_ ev_timer *w, int revents)
864	{	1152	{
865	struct my_biggy big = (struct my_biggy *	1153	struct my_biggy big = (struct my_biggy *
866	(((char *)w) - offsetof (struct my_biggy, t1));	1154	(((char *)w) - offsetof (struct my_biggy, t1));
867	}	1155	}
868		1156
869	static void	1157	static void
870	t2_cb (EV_P_ struct ev_timer *w, int revents)	1158	t2_cb (EV_P_ ev_timer *w, int revents)
871	{	1159	{
872	struct my_biggy big = (struct my_biggy *	1160	struct my_biggy big = (struct my_biggy *
873	(((char *)w) - offsetof (struct my_biggy, t2));	1161	(((char *)w) - offsetof (struct my_biggy, t2));
874	}	1162	}
875		1163
876		1164
877	=head1 WATCHER TYPES	1165	=head1 WATCHER TYPES
878		1166
879	This section describes each watcher in detail, but will not repeat	1167	This section describes each watcher in detail, but will not repeat
…		…
903	In general you can register as many read and/or write event watchers per	1191	In general you can register as many read and/or write event watchers per
904	fd as you want (as long as you don't confuse yourself). Setting all file	1192	fd as you want (as long as you don't confuse yourself). Setting all file
905	descriptors to non-blocking mode is also usually a good idea (but not	1193	descriptors to non-blocking mode is also usually a good idea (but not
906	required if you know what you are doing).	1194	required if you know what you are doing).
907		1195
908	You have to be careful with dup'ed file descriptors, though. Some backends	1196	If you cannot use non-blocking mode, then force the use of a
909	(the linux epoll backend is a notable example) cannot handle dup'ed file	1197	known-to-be-good backend (at the time of this writing, this includes only
910	descriptors correctly if you register interest in two or more fds pointing	1198	C<EVBACKEND_SELECT> and C<EVBACKEND_POLL>).
911	to the same underlying file/socket/etc. description (that is, they share
912	the same underlying "file open").
913
914	If you must do this, then force the use of a known-to-be-good backend
915	(at the time of this writing, this includes only C<EVBACKEND_SELECT> and
916	C<EVBACKEND_POLL>).
917		1199
918	Another thing you have to watch out for is that it is quite easy to	1200	Another thing you have to watch out for is that it is quite easy to
919	receive "spurious" readyness notifications, that is your callback might	1201	receive "spurious" readiness notifications, that is your callback might
920	be called with C<EV_READ> but a subsequent C<read>(2) will actually block	1202	be called with C<EV_READ> but a subsequent C<read>(2) will actually block
921	because there is no data. Not only are some backends known to create a	1203	because there is no data. Not only are some backends known to create a
922	lot of those (for example solaris ports), it is very easy to get into	1204	lot of those (for example Solaris ports), it is very easy to get into
923	this situation even with a relatively standard program structure. Thus	1205	this situation even with a relatively standard program structure. Thus
924	it is best to always use non-blocking I/O: An extra C<read>(2) returning	1206	it is best to always use non-blocking I/O: An extra C<read>(2) returning
925	C<EAGAIN> is far preferable to a program hanging until some data arrives.	1207	C<EAGAIN> is far preferable to a program hanging until some data arrives.
926		1208
927	If you cannot run the fd in non-blocking mode (for example you should not	1209	If you cannot run the fd in non-blocking mode (for example you should
928	play around with an Xlib connection), then you have to seperately re-test	1210	not play around with an Xlib connection), then you have to separately
929	whether a file descriptor is really ready with a known-to-be good interface	1211	re-test whether a file descriptor is really ready with a known-to-be good
930	such as poll (fortunately in our Xlib example, Xlib already does this on	1212	interface such as poll (fortunately in our Xlib example, Xlib already
931	its own, so its quite safe to use).	1213	does this on its own, so its quite safe to use). Some people additionally
		1214	use C<SIGALRM> and an interval timer, just to be sure you won't block
		1215	indefinitely.
		1216
		1217	But really, best use non-blocking mode.
932		1218
933	=head3 The special problem of disappearing file descriptors	1219	=head3 The special problem of disappearing file descriptors
934		1220
935	Some backends (e.g. kqueue, epoll) need to be told about closing a file	1221	Some backends (e.g. kqueue, epoll) need to be told about closing a file
936	descriptor (either by calling C<close> explicitly or by any other means,	1222	descriptor (either due to calling C<close> explicitly or any other means,
937	such as C<dup>). The reason is that you register interest in some file	1223	such as C<dup2>). The reason is that you register interest in some file
938	descriptor, but when it goes away, the operating system will silently drop	1224	descriptor, but when it goes away, the operating system will silently drop
939	this interest. If another file descriptor with the same number then is	1225	this interest. If another file descriptor with the same number then is
940	registered with libev, there is no efficient way to see that this is, in	1226	registered with libev, there is no efficient way to see that this is, in
941	fact, a different file descriptor.	1227	fact, a different file descriptor.
942		1228
…		…
949		1235
950	This is how one would do it normally anyway, the important point is that	1236	This is how one would do it normally anyway, the important point is that
951	the libev application should not optimise around libev but should leave	1237	the libev application should not optimise around libev but should leave
952	optimisations to libev.	1238	optimisations to libev.
953		1239
954	=head3 Ths special problem of dup'ed file descriptors	1240	=head3 The special problem of dup'ed file descriptors
955		1241
956	Some backends (e.g. epoll), cannot register events for file descriptors,	1242	Some backends (e.g. epoll), cannot register events for file descriptors,
957	but only events for the underlying file descriptions. That menas when you	1243	but only events for the underlying file descriptions. That means when you
958	have C<dup ()>'ed file descriptors and register events for them, only one	1244	have C<dup ()>'ed file descriptors or weirder constellations, and register
959	file descriptor might actually receive events.	1245	events for them, only one file descriptor might actually receive events.
960		1246
961	There is no workaorund possible except not registering events	1247	There is no workaround possible except not registering events
962	for potentially C<dup ()>'ed file descriptors or to resort to	1248	for potentially C<dup ()>'ed file descriptors, or to resort to
963	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.	1249	C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
964		1250
965	=head3 The special problem of fork	1251	=head3 The special problem of fork
966		1252
967	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit	1253	Some backends (epoll, kqueue) do not support C<fork ()> at all or exhibit
…		…
971	To support fork in your programs, you either have to call	1257	To support fork in your programs, you either have to call
972	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,	1258	C<ev_default_fork ()> or C<ev_loop_fork ()> after a fork in the child,
973	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or	1259	enable C<EVFLAG_FORKCHECK>, or resort to C<EVBACKEND_SELECT> or
974	C<EVBACKEND_POLL>.	1260	C<EVBACKEND_POLL>.
975		1261
		1262	=head3 The special problem of SIGPIPE
		1263
		1264	While not really specific to libev, it is easy to forget about C<SIGPIPE>:
		1265	when writing to a pipe whose other end has been closed, your program gets
		1266	sent a SIGPIPE, which, by default, aborts your program. For most programs
		1267	this is sensible behaviour, for daemons, this is usually undesirable.
		1268
		1269	So when you encounter spurious, unexplained daemon exits, make sure you
		1270	ignore SIGPIPE (and maybe make sure you log the exit status of your daemon
		1271	somewhere, as that would have given you a big clue).
		1272
976		1273
977	=head3 Watcher-Specific Functions	1274	=head3 Watcher-Specific Functions
978		1275
979	=over 4	1276	=over 4
980		1277
981	=item ev_io_init (ev_io *, callback, int fd, int events)	1278	=item ev_io_init (ev_io *, callback, int fd, int events)
982		1279
983	=item ev_io_set (ev_io *, int fd, int events)	1280	=item ev_io_set (ev_io *, int fd, int events)
984		1281
985	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to	1282	Configures an C<ev_io> watcher. The C<fd> is the file descriptor to
986	rceeive events for and events is either C<EV_READ>, C<EV_WRITE> or	1283	receive events for and C<events> is either C<EV_READ>, C<EV_WRITE> or
987	C<EV_READ | EV_WRITE> to receive the given events.	1284	C<EV_READ | EV_WRITE>, to express the desire to receive the given events.
988		1285
989	=item int fd [read-only]	1286	=item int fd [read-only]
990		1287
991	The file descriptor being watched.	1288	The file descriptor being watched.
992		1289
993	=item int events [read-only]	1290	=item int events [read-only]
994		1291
995	The events being watched.	1292	The events being watched.
996		1293
997	=back	1294	=back
		1295
		1296	=head3 Examples
998		1297
999	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well	1298	Example: Call C<stdin_readable_cb> when STDIN_FILENO has become, well
1000	readable, but only once. Since it is likely line-buffered, you could	1299	readable, but only once. Since it is likely line-buffered, you could
1001	attempt to read a whole line in the callback.	1300	attempt to read a whole line in the callback.
1002		1301
1003	static void	1302	static void
1004	stdin_readable_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1303	stdin_readable_cb (struct ev_loop *loop, ev_io *w, int revents)
1005	{	1304	{
1006	ev_io_stop (loop, w);	1305	ev_io_stop (loop, w);
1007	.. read from stdin here (or from w->fd) and haqndle any I/O errors	1306	.. read from stdin here (or from w->fd) and handle any I/O errors
1008	}	1307	}
1009		1308
1010	...	1309	...
1011	struct ev_loop *loop = ev_default_init (0);	1310	struct ev_loop *loop = ev_default_init (0);
1012	struct ev_io stdin_readable;	1311	ev_io stdin_readable;
1013	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);	1312	ev_io_init (&stdin_readable, stdin_readable_cb, STDIN_FILENO, EV_READ);
1014	ev_io_start (loop, &stdin_readable);	1313	ev_io_start (loop, &stdin_readable);
1015	ev_loop (loop, 0);	1314	ev_loop (loop, 0);
1016		1315
1017		1316
1018	=head2 C<ev_timer> - relative and optionally repeating timeouts	1317	=head2 C<ev_timer> - relative and optionally repeating timeouts
1019		1318
1020	Timer watchers are simple relative timers that generate an event after a	1319	Timer watchers are simple relative timers that generate an event after a
1021	given time, and optionally repeating in regular intervals after that.	1320	given time, and optionally repeating in regular intervals after that.
1022		1321
1023	The timers are based on real time, that is, if you register an event that	1322	The timers are based on real time, that is, if you register an event that
1024	times out after an hour and you reset your system clock to last years	1323	times out after an hour and you reset your system clock to January last
1025	time, it will still time out after (roughly) and hour. "Roughly" because	1324	year, it will still time out after (roughly) one hour. "Roughly" because
1026	detecting time jumps is hard, and some inaccuracies are unavoidable (the	1325	detecting time jumps is hard, and some inaccuracies are unavoidable (the
1027	monotonic clock option helps a lot here).	1326	monotonic clock option helps a lot here).
		1327
		1328	The callback is guaranteed to be invoked only I<after> its timeout has
		1329	passed, but if multiple timers become ready during the same loop iteration
		1330	then order of execution is undefined.
		1331
		1332	=head3 Be smart about timeouts
		1333
		1334	Many real-world problems involve some kind of timeout, usually for error
		1335	recovery. A typical example is an HTTP request - if the other side hangs,
		1336	you want to raise some error after a while.
		1337
		1338	What follows are some ways to handle this problem, from obvious and
		1339	inefficient to smart and efficient.
		1340
		1341	In the following, a 60 second activity timeout is assumed - a timeout that
		1342	gets reset to 60 seconds each time there is activity (e.g. each time some
		1343	data or other life sign was received).
		1344
		1345	=over 4
		1346
		1347	=item 1. Use a timer and stop, reinitialise and start it on activity.
		1348
		1349	This is the most obvious, but not the most simple way: In the beginning,
		1350	start the watcher:
		1351
		1352	ev_timer_init (timer, callback, 60., 0.);
		1353	ev_timer_start (loop, timer);
		1354
		1355	Then, each time there is some activity, C<ev_timer_stop> it, initialise it
		1356	and start it again:
		1357
		1358	ev_timer_stop (loop, timer);
		1359	ev_timer_set (timer, 60., 0.);
		1360	ev_timer_start (loop, timer);
		1361
		1362	This is relatively simple to implement, but means that each time there is
		1363	some activity, libev will first have to remove the timer from its internal
		1364	data structure and then add it again. Libev tries to be fast, but it's
		1365	still not a constant-time operation.
		1366
		1367	=item 2. Use a timer and re-start it with C<ev_timer_again> inactivity.
		1368
		1369	This is the easiest way, and involves using C<ev_timer_again> instead of
		1370	C<ev_timer_start>.
		1371
		1372	To implement this, configure an C<ev_timer> with a C<repeat> value
		1373	of C<60> and then call C<ev_timer_again> at start and each time you
		1374	successfully read or write some data. If you go into an idle state where
		1375	you do not expect data to travel on the socket, you can C<ev_timer_stop>
		1376	the timer, and C<ev_timer_again> will automatically restart it if need be.
		1377
		1378	That means you can ignore both the C<ev_timer_start> function and the
		1379	C<after> argument to C<ev_timer_set>, and only ever use the C<repeat>
		1380	member and C<ev_timer_again>.
		1381
		1382	At start:
		1383
		1384	ev_timer_init (timer, callback);
		1385	timer->repeat = 60.;
		1386	ev_timer_again (loop, timer);
		1387
		1388	Each time there is some activity:
		1389
		1390	ev_timer_again (loop, timer);
		1391
		1392	It is even possible to change the time-out on the fly, regardless of
		1393	whether the watcher is active or not:
		1394
		1395	timer->repeat = 30.;
		1396	ev_timer_again (loop, timer);
		1397
		1398	This is slightly more efficient then stopping/starting the timer each time
		1399	you want to modify its timeout value, as libev does not have to completely
		1400	remove and re-insert the timer from/into its internal data structure.
		1401
		1402	It is, however, even simpler than the "obvious" way to do it.
		1403
		1404	=item 3. Let the timer time out, but then re-arm it as required.
		1405
		1406	This method is more tricky, but usually most efficient: Most timeouts are
		1407	relatively long compared to the intervals between other activity - in
		1408	our example, within 60 seconds, there are usually many I/O events with
		1409	associated activity resets.
		1410
		1411	In this case, it would be more efficient to leave the C<ev_timer> alone,
		1412	but remember the time of last activity, and check for a real timeout only
		1413	within the callback:
		1414
		1415	ev_tstamp last_activity; // time of last activity
		1416
		1417	static void
		1418	callback (EV_P_ ev_timer *w, int revents)
		1419	{
		1420	ev_tstamp now = ev_now (EV_A);
		1421	ev_tstamp timeout = last_activity + 60.;
		1422
		1423	// if last_activity + 60. is older than now, we did time out
		1424	if (timeout < now)
		1425	{
		1426	// timeout occured, take action
		1427	}
		1428	else
		1429	{
		1430	// callback was invoked, but there was some activity, re-arm
		1431	// the watcher to fire in last_activity + 60, which is
		1432	// guaranteed to be in the future, so "again" is positive:
		1433	w->repeat = timeout - now;
		1434	ev_timer_again (EV_A_ w);
		1435	}
		1436	}
		1437
		1438	To summarise the callback: first calculate the real timeout (defined
		1439	as "60 seconds after the last activity"), then check if that time has
		1440	been reached, which means something I<did>, in fact, time out. Otherwise
		1441	the callback was invoked too early (C<timeout> is in the future), so
		1442	re-schedule the timer to fire at that future time, to see if maybe we have
		1443	a timeout then.
		1444
		1445	Note how C<ev_timer_again> is used, taking advantage of the
		1446	C<ev_timer_again> optimisation when the timer is already running.
		1447
		1448	This scheme causes more callback invocations (about one every 60 seconds
		1449	minus half the average time between activity), but virtually no calls to
		1450	libev to change the timeout.
		1451
		1452	To start the timer, simply initialise the watcher and set C<last_activity>
		1453	to the current time (meaning we just have some activity :), then call the
		1454	callback, which will "do the right thing" and start the timer:
		1455
		1456	ev_timer_init (timer, callback);
		1457	last_activity = ev_now (loop);
		1458	callback (loop, timer, EV_TIMEOUT);
		1459
		1460	And when there is some activity, simply store the current time in
		1461	C<last_activity>, no libev calls at all:
		1462
		1463	last_actiivty = ev_now (loop);
		1464
		1465	This technique is slightly more complex, but in most cases where the
		1466	time-out is unlikely to be triggered, much more efficient.
		1467
		1468	Changing the timeout is trivial as well (if it isn't hard-coded in the
		1469	callback :) - just change the timeout and invoke the callback, which will
		1470	fix things for you.
		1471
		1472	=item 4. Wee, just use a double-linked list for your timeouts.
		1473
		1474	If there is not one request, but many thousands (millions...), all
		1475	employing some kind of timeout with the same timeout value, then one can
		1476	do even better:
		1477
		1478	When starting the timeout, calculate the timeout value and put the timeout
		1479	at the I<end> of the list.
		1480
		1481	Then use an C<ev_timer> to fire when the timeout at the I<beginning> of
		1482	the list is expected to fire (for example, using the technique #3).
		1483
		1484	When there is some activity, remove the timer from the list, recalculate
		1485	the timeout, append it to the end of the list again, and make sure to
		1486	update the C<ev_timer> if it was taken from the beginning of the list.
		1487
		1488	This way, one can manage an unlimited number of timeouts in O(1) time for
		1489	starting, stopping and updating the timers, at the expense of a major
		1490	complication, and having to use a constant timeout. The constant timeout
		1491	ensures that the list stays sorted.
		1492
		1493	=back
		1494
		1495	So which method the best?
		1496
		1497	Method #2 is a simple no-brain-required solution that is adequate in most
		1498	situations. Method #3 requires a bit more thinking, but handles many cases
		1499	better, and isn't very complicated either. In most case, choosing either
		1500	one is fine, with #3 being better in typical situations.
		1501
		1502	Method #1 is almost always a bad idea, and buys you nothing. Method #4 is
		1503	rather complicated, but extremely efficient, something that really pays
		1504	off after the first million or so of active timers, i.e. it's usually
		1505	overkill :)
		1506
		1507	=head3 The special problem of time updates
		1508
		1509	Establishing the current time is a costly operation (it usually takes at
		1510	least two system calls): EV therefore updates its idea of the current
		1511	time only before and after C<ev_loop> collects new events, which causes a
		1512	growing difference between C<ev_now ()> and C<ev_time ()> when handling
		1513	lots of events in one iteration.
1028		1514
1029	The relative timeouts are calculated relative to the C<ev_now ()>	1515	The relative timeouts are calculated relative to the C<ev_now ()>
1030	time. This is usually the right thing as this timestamp refers to the time	1516	time. This is usually the right thing as this timestamp refers to the time
1031	of the event triggering whatever timeout you are modifying/starting. If	1517	of the event triggering whatever timeout you are modifying/starting. If
1032	you suspect event processing to be delayed and you I<need> to base the timeout	1518	you suspect event processing to be delayed and you I<need> to base the
1033	on the current time, use something like this to adjust for this:	1519	timeout on the current time, use something like this to adjust for this:
1034		1520
1035	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);	1521	ev_timer_set (&timer, after + ev_now () - ev_time (), 0.);
1036		1522
1037	The callback is guarenteed to be invoked only when its timeout has passed,	1523	If the event loop is suspended for a long time, you can also force an
1038	but if multiple timers become ready during the same loop iteration then	1524	update of the time returned by C<ev_now ()> by calling C<ev_now_update
1039	order of execution is undefined.	1525	()>.
1040		1526
1041	=head3 Watcher-Specific Functions and Data Members	1527	=head3 Watcher-Specific Functions and Data Members
1042		1528
1043	=over 4	1529	=over 4
1044		1530
1045	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)	1531	=item ev_timer_init (ev_timer *, callback, ev_tstamp after, ev_tstamp repeat)
1046		1532
1047	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)	1533	=item ev_timer_set (ev_timer *, ev_tstamp after, ev_tstamp repeat)
1048		1534
1049	Configure the timer to trigger after C<after> seconds. If C<repeat> is	1535	Configure the timer to trigger after C<after> seconds. If C<repeat>
1050	C<0.>, then it will automatically be stopped. If it is positive, then the	1536	is C<0.>, then it will automatically be stopped once the timeout is
1051	timer will automatically be configured to trigger again C<repeat> seconds	1537	reached. If it is positive, then the timer will automatically be
1052	later, again, and again, until stopped manually.	1538	configured to trigger again C<repeat> seconds later, again, and again,
		1539	until stopped manually.
1053		1540
1054	The timer itself will do a best-effort at avoiding drift, that is, if you	1541	The timer itself will do a best-effort at avoiding drift, that is, if
1055	configure a timer to trigger every 10 seconds, then it will trigger at	1542	you configure a timer to trigger every 10 seconds, then it will normally
1056	exactly 10 second intervals. If, however, your program cannot keep up with	1543	trigger at exactly 10 second intervals. If, however, your program cannot
1057	the timer (because it takes longer than those 10 seconds to do stuff) the	1544	keep up with the timer (because it takes longer than those 10 seconds to
1058	timer will not fire more than once per event loop iteration.	1545	do stuff) the timer will not fire more than once per event loop iteration.
1059		1546
1060	=item ev_timer_again (loop)	1547	=item ev_timer_again (loop, ev_timer *)
1061		1548
1062	This will act as if the timer timed out and restart it again if it is	1549	This will act as if the timer timed out and restart it again if it is
1063	repeating. The exact semantics are:	1550	repeating. The exact semantics are:
1064		1551
1065	If the timer is pending, its pending status is cleared.	1552	If the timer is pending, its pending status is cleared.
1066		1553
1067	If the timer is started but nonrepeating, stop it (as if it timed out).	1554	If the timer is started but non-repeating, stop it (as if it timed out).
1068		1555
1069	If the timer is repeating, either start it if necessary (with the	1556	If the timer is repeating, either start it if necessary (with the
1070	C<repeat> value), or reset the running timer to the C<repeat> value.	1557	C<repeat> value), or reset the running timer to the C<repeat> value.
1071		1558
1072	This sounds a bit complicated, but here is a useful and typical	1559	This sounds a bit complicated, see "Be smart about timeouts", above, for a
1073	example: Imagine you have a tcp connection and you want a so-called idle	1560	usage example.
1074	timeout, that is, you want to be called when there have been, say, 60
1075	seconds of inactivity on the socket. The easiest way to do this is to
1076	configure an C<ev_timer> with a C<repeat> value of C<60> and then call
1077	C<ev_timer_again> each time you successfully read or write some data. If
1078	you go into an idle state where you do not expect data to travel on the
1079	socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
1080	automatically restart it if need be.
1081
1082	That means you can ignore the C<after> value and C<ev_timer_start>
1083	altogether and only ever use the C<repeat> value and C<ev_timer_again>:
1084
1085	ev_timer_init (timer, callback, 0., 5.);
1086	ev_timer_again (loop, timer);
1087	...
1088	timer->again = 17.;
1089	ev_timer_again (loop, timer);
1090	...
1091	timer->again = 10.;
1092	ev_timer_again (loop, timer);
1093
1094	This is more slightly efficient then stopping/starting the timer each time
1095	you want to modify its timeout value.
1096		1561
1097	=item ev_tstamp repeat [read-write]	1562	=item ev_tstamp repeat [read-write]
1098		1563
1099	The current C<repeat> value. Will be used each time the watcher times out	1564	The current C<repeat> value. Will be used each time the watcher times out
1100	or C<ev_timer_again> is called and determines the next timeout (if any),	1565	or C<ev_timer_again> is called, and determines the next timeout (if any),
1101	which is also when any modifications are taken into account.	1566	which is also when any modifications are taken into account.
1102		1567
1103	=back	1568	=back
1104		1569
		1570	=head3 Examples
		1571
1105	Example: Create a timer that fires after 60 seconds.	1572	Example: Create a timer that fires after 60 seconds.
1106		1573
1107	static void	1574	static void
1108	one_minute_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1575	one_minute_cb (struct ev_loop *loop, ev_timer *w, int revents)
1109	{	1576	{
1110	.. one minute over, w is actually stopped right here	1577	.. one minute over, w is actually stopped right here
1111	}	1578	}
1112		1579
1113	struct ev_timer mytimer;	1580	ev_timer mytimer;
1114	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);	1581	ev_timer_init (&mytimer, one_minute_cb, 60., 0.);
1115	ev_timer_start (loop, &mytimer);	1582	ev_timer_start (loop, &mytimer);
1116		1583
1117	Example: Create a timeout timer that times out after 10 seconds of	1584	Example: Create a timeout timer that times out after 10 seconds of
1118	inactivity.	1585	inactivity.
1119		1586
1120	static void	1587	static void
1121	timeout_cb (struct ev_loop *loop, struct ev_timer *w, int revents)	1588	timeout_cb (struct ev_loop *loop, ev_timer *w, int revents)
1122	{	1589	{
1123	.. ten seconds without any activity	1590	.. ten seconds without any activity
1124	}	1591	}
1125		1592
1126	struct ev_timer mytimer;	1593	ev_timer mytimer;
1127	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */	1594	ev_timer_init (&mytimer, timeout_cb, 0., 10.); /* note, only repeat used */
1128	ev_timer_again (&mytimer); /* start timer */	1595	ev_timer_again (&mytimer); /* start timer */
1129	ev_loop (loop, 0);	1596	ev_loop (loop, 0);
1130		1597
1131	// and in some piece of code that gets executed on any "activity":	1598	// and in some piece of code that gets executed on any "activity":
1132	// reset the timeout to start ticking again at 10 seconds	1599	// reset the timeout to start ticking again at 10 seconds
1133	ev_timer_again (&mytimer);	1600	ev_timer_again (&mytimer);
1134		1601
1135		1602
1136	=head2 C<ev_periodic> - to cron or not to cron?	1603	=head2 C<ev_periodic> - to cron or not to cron?
1137		1604
1138	Periodic watchers are also timers of a kind, but they are very versatile	1605	Periodic watchers are also timers of a kind, but they are very versatile
1139	(and unfortunately a bit complex).	1606	(and unfortunately a bit complex).
1140		1607
1141	Unlike C<ev_timer>'s, they are not based on real time (or relative time)	1608	Unlike C<ev_timer>, periodic watchers are not based on real time (or
1142	but on wallclock time (absolute time). You can tell a periodic watcher	1609	relative time, the physical time that passes) but on wall clock time
1143	to trigger "at" some specific point in time. For example, if you tell a	1610	(absolute time, the thing you can read on your calender or clock). The
1144	periodic watcher to trigger in 10 seconds (by specifiying e.g. C<ev_now ()	1611	difference is that wall clock time can run faster or slower than real
1145	+ 10.>) and then reset your system clock to the last year, then it will	1612	time, and time jumps are not uncommon (e.g. when you adjust your
1146	take a year to trigger the event (unlike an C<ev_timer>, which would trigger	1613	wrist-watch).
1147	roughly 10 seconds later).
1148		1614
1149	They can also be used to implement vastly more complex timers, such as	1615	You can tell a periodic watcher to trigger after some specific point
1150	triggering an event on each midnight, local time or other, complicated,	1616	in time: for example, if you tell a periodic watcher to trigger "in 10
1151	rules.	1617	seconds" (by specifying e.g. C<ev_now () + 10.>, that is, an absolute time
		1618	not a delay) and then reset your system clock to January of the previous
		1619	year, then it will take a year or more to trigger the event (unlike an
		1620	C<ev_timer>, which would still trigger roughly 10 seconds after starting
		1621	it, as it uses a relative timeout).
1152		1622
		1623	C<ev_periodic> watchers can also be used to implement vastly more complex
		1624	timers, such as triggering an event on each "midnight, local time", or
		1625	other complicated rules. This cannot be done with C<ev_timer> watchers, as
		1626	those cannot react to time jumps.
		1627
1153	As with timers, the callback is guarenteed to be invoked only when the	1628	As with timers, the callback is guaranteed to be invoked only when the
1154	time (C<at>) has been passed, but if multiple periodic timers become ready	1629	point in time where it is supposed to trigger has passed, but if multiple
1155	during the same loop iteration then order of execution is undefined.	1630	periodic timers become ready during the same loop iteration, then order of
		1631	execution is undefined.
1156		1632
1157	=head3 Watcher-Specific Functions and Data Members	1633	=head3 Watcher-Specific Functions and Data Members
1158		1634
1159	=over 4	1635	=over 4
1160		1636
1161	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp at, ev_tstamp interval, reschedule_cb)	1637	=item ev_periodic_init (ev_periodic *, callback, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1162		1638
1163	=item ev_periodic_set (ev_periodic *, ev_tstamp after, ev_tstamp repeat, reschedule_cb)	1639	=item ev_periodic_set (ev_periodic *, ev_tstamp offset, ev_tstamp interval, reschedule_cb)
1164		1640
1165	Lots of arguments, lets sort it out... There are basically three modes of	1641	Lots of arguments, let's sort it out... There are basically three modes of
1166	operation, and we will explain them from simplest to complex:	1642	operation, and we will explain them from simplest to most complex:
1167		1643
1168	=over 4	1644	=over 4
1169		1645
1170	=item * absolute timer (at = time, interval = reschedule_cb = 0)	1646	=item * absolute timer (offset = absolute time, interval = 0, reschedule_cb = 0)
1171		1647
1172	In this configuration the watcher triggers an event at the wallclock time	1648	In this configuration the watcher triggers an event after the wall clock
1173	C<at> and doesn't repeat. It will not adjust when a time jump occurs,	1649	time C<offset> has passed. It will not repeat and will not adjust when a
1174	that is, if it is to be run at January 1st 2011 then it will run when the	1650	time jump occurs, that is, if it is to be run at January 1st 2011 then it
1175	system time reaches or surpasses this time.	1651	will be stopped and invoked when the system clock reaches or surpasses
		1652	this point in time.
1176		1653
1177	=item * non-repeating interval timer (at = offset, interval > 0, reschedule_cb = 0)	1654	=item * repeating interval timer (offset = offset within interval, interval > 0, reschedule_cb = 0)
1178		1655
1179	In this mode the watcher will always be scheduled to time out at the next	1656	In this mode the watcher will always be scheduled to time out at the next
1180	C<at + N * interval> time (for some integer N, which can also be negative)	1657	C<offset + N * interval> time (for some integer N, which can also be
1181	and then repeat, regardless of any time jumps.	1658	negative) and then repeat, regardless of any time jumps. The C<offset>
		1659	argument is merely an offset into the C<interval> periods.
1182		1660
1183	This can be used to create timers that do not drift with respect to system	1661	This can be used to create timers that do not drift with respect to the
1184	time:	1662	system clock, for example, here is an C<ev_periodic> that triggers each
		1663	hour, on the hour (with respect to UTC):
1185		1664
1186	ev_periodic_set (&periodic, 0., 3600., 0);	1665	ev_periodic_set (&periodic, 0., 3600., 0);
1187		1666
1188	This doesn't mean there will always be 3600 seconds in between triggers,	1667	This doesn't mean there will always be 3600 seconds in between triggers,
1189	but only that the the callback will be called when the system time shows a	1668	but only that the callback will be called when the system time shows a
1190	full hour (UTC), or more correctly, when the system time is evenly divisible	1669	full hour (UTC), or more correctly, when the system time is evenly divisible
1191	by 3600.	1670	by 3600.
1192		1671
1193	Another way to think about it (for the mathematically inclined) is that	1672	Another way to think about it (for the mathematically inclined) is that
1194	C<ev_periodic> will try to run the callback in this mode at the next possible	1673	C<ev_periodic> will try to run the callback in this mode at the next possible
1195	time where C<time = at (mod interval)>, regardless of any time jumps.	1674	time where C<time = offset (mod interval)>, regardless of any time jumps.
1196		1675
1197	For numerical stability it is preferable that the C<at> value is near	1676	For numerical stability it is preferable that the C<offset> value is near
1198	C<ev_now ()> (the current time), but there is no range requirement for	1677	C<ev_now ()> (the current time), but there is no range requirement for
1199	this value.	1678	this value, and in fact is often specified as zero.
1200		1679
		1680	Note also that there is an upper limit to how often a timer can fire (CPU
		1681	speed for example), so if C<interval> is very small then timing stability
		1682	will of course deteriorate. Libev itself tries to be exact to be about one
		1683	millisecond (if the OS supports it and the machine is fast enough).
		1684
1201	=item * manual reschedule mode (at and interval ignored, reschedule_cb = callback)	1685	=item * manual reschedule mode (offset ignored, interval ignored, reschedule_cb = callback)
1202		1686
1203	In this mode the values for C<interval> and C<at> are both being	1687	In this mode the values for C<interval> and C<offset> are both being
1204	ignored. Instead, each time the periodic watcher gets scheduled, the	1688	ignored. Instead, each time the periodic watcher gets scheduled, the
1205	reschedule callback will be called with the watcher as first, and the	1689	reschedule callback will be called with the watcher as first, and the
1206	current time as second argument.	1690	current time as second argument.
1207		1691
1208	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher,	1692	NOTE: I<This callback MUST NOT stop or destroy any periodic watcher, ever,
1209	ever, or make any event loop modifications>. If you need to stop it,	1693	or make ANY other event loop modifications whatsoever, unless explicitly
1210	return C<now + 1e30> (or so, fudge fudge) and stop it afterwards (e.g. by	1694	allowed by documentation here>.
1211	starting an C<ev_prepare> watcher, which is legal).
1212		1695
		1696	If you need to stop it, return C<now + 1e30> (or so, fudge fudge) and stop
		1697	it afterwards (e.g. by starting an C<ev_prepare> watcher, which is the
		1698	only event loop modification you are allowed to do).
		1699
1213	Its prototype is C<ev_tstamp (*reschedule_cb)(struct ev_periodic *w,	1700	The callback prototype is C<ev_tstamp (*reschedule_cb)(ev_periodic
1214	ev_tstamp now)>, e.g.:	1701	*w, ev_tstamp now)>, e.g.:
1215		1702
		1703	static ev_tstamp
1216	static ev_tstamp my_rescheduler (struct ev_periodic *w, ev_tstamp now)	1704	my_rescheduler (ev_periodic *w, ev_tstamp now)
1217	{	1705	{
1218	return now + 60.;	1706	return now + 60.;
1219	}	1707	}
1220		1708
1221	It must return the next time to trigger, based on the passed time value	1709	It must return the next time to trigger, based on the passed time value
1222	(that is, the lowest time value larger than to the second argument). It	1710	(that is, the lowest time value larger than to the second argument). It
1223	will usually be called just before the callback will be triggered, but	1711	will usually be called just before the callback will be triggered, but
1224	might be called at other times, too.	1712	might be called at other times, too.
1225		1713
1226	NOTE: I<< This callback must always return a time that is later than the	1714	NOTE: I<< This callback must always return a time that is higher than or
1227	passed C<now> value >>. Not even C<now> itself will do, it I<must> be larger.	1715	equal to the passed C<now> value >>.
1228		1716
1229	This can be used to create very complex timers, such as a timer that	1717	This can be used to create very complex timers, such as a timer that
1230	triggers on each midnight, local time. To do this, you would calculate the	1718	triggers on "next midnight, local time". To do this, you would calculate the
1231	next midnight after C<now> and return the timestamp value for this. How	1719	next midnight after C<now> and return the timestamp value for this. How
1232	you do this is, again, up to you (but it is not trivial, which is the main	1720	you do this is, again, up to you (but it is not trivial, which is the main
1233	reason I omitted it as an example).	1721	reason I omitted it as an example).
1234		1722
1235	=back	1723	=back
…		…
1239	Simply stops and restarts the periodic watcher again. This is only useful	1727	Simply stops and restarts the periodic watcher again. This is only useful
1240	when you changed some parameters or the reschedule callback would return	1728	when you changed some parameters or the reschedule callback would return
1241	a different time than the last time it was called (e.g. in a crond like	1729	a different time than the last time it was called (e.g. in a crond like
1242	program when the crontabs have changed).	1730	program when the crontabs have changed).
1243		1731
		1732	=item ev_tstamp ev_periodic_at (ev_periodic *)
		1733
		1734	When active, returns the absolute time that the watcher is supposed
		1735	to trigger next. This is not the same as the C<offset> argument to
		1736	C<ev_periodic_set>, but indeed works even in interval and manual
		1737	rescheduling modes.
		1738
1244	=item ev_tstamp offset [read-write]	1739	=item ev_tstamp offset [read-write]
1245		1740
1246	When repeating, this contains the offset value, otherwise this is the	1741	When repeating, this contains the offset value, otherwise this is the
1247	absolute point in time (the C<at> value passed to C<ev_periodic_set>).	1742	absolute point in time (the C<offset> value passed to C<ev_periodic_set>,
		1743	although libev might modify this value for better numerical stability).
1248		1744
1249	Can be modified any time, but changes only take effect when the periodic	1745	Can be modified any time, but changes only take effect when the periodic
1250	timer fires or C<ev_periodic_again> is being called.	1746	timer fires or C<ev_periodic_again> is being called.
1251		1747
1252	=item ev_tstamp interval [read-write]	1748	=item ev_tstamp interval [read-write]
1253		1749
1254	The current interval value. Can be modified any time, but changes only	1750	The current interval value. Can be modified any time, but changes only
1255	take effect when the periodic timer fires or C<ev_periodic_again> is being	1751	take effect when the periodic timer fires or C<ev_periodic_again> is being
1256	called.	1752	called.
1257		1753
1258	=item ev_tstamp (*reschedule_cb)(struct ev_periodic *w, ev_tstamp now) [read-write]	1754	=item ev_tstamp (*reschedule_cb)(ev_periodic *w, ev_tstamp now) [read-write]
1259		1755
1260	The current reschedule callback, or C<0>, if this functionality is	1756	The current reschedule callback, or C<0>, if this functionality is
1261	switched off. Can be changed any time, but changes only take effect when	1757	switched off. Can be changed any time, but changes only take effect when
1262	the periodic timer fires or C<ev_periodic_again> is being called.	1758	the periodic timer fires or C<ev_periodic_again> is being called.
1263		1759
1264	=item ev_tstamp at [read-only]
1265
1266	When active, contains the absolute time that the watcher is supposed to
1267	trigger next.
1268
1269	=back	1760	=back
1270		1761
		1762	=head3 Examples
		1763
1271	Example: Call a callback every hour, or, more precisely, whenever the	1764	Example: Call a callback every hour, or, more precisely, whenever the
1272	system clock is divisible by 3600. The callback invocation times have	1765	system time is divisible by 3600. The callback invocation times have
1273	potentially a lot of jittering, but good long-term stability.	1766	potentially a lot of jitter, but good long-term stability.
1274		1767
1275	static void	1768	static void
1276	clock_cb (struct ev_loop *loop, struct ev_io *w, int revents)	1769	clock_cb (struct ev_loop *loop, ev_io *w, int revents)
1277	{	1770	{
1278	... its now a full hour (UTC, or TAI or whatever your clock follows)	1771	... its now a full hour (UTC, or TAI or whatever your clock follows)
1279	}	1772	}
1280		1773
1281	struct ev_periodic hourly_tick;	1774	ev_periodic hourly_tick;
1282	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);	1775	ev_periodic_init (&hourly_tick, clock_cb, 0., 3600., 0);
1283	ev_periodic_start (loop, &hourly_tick);	1776	ev_periodic_start (loop, &hourly_tick);
1284		1777
1285	Example: The same as above, but use a reschedule callback to do it:	1778	Example: The same as above, but use a reschedule callback to do it:
1286		1779
1287	#include <math.h>	1780	#include <math.h>
1288		1781
1289	static ev_tstamp	1782	static ev_tstamp
1290	my_scheduler_cb (struct ev_periodic *w, ev_tstamp now)	1783	my_scheduler_cb (ev_periodic *w, ev_tstamp now)
1291	{	1784	{
1292	return fmod (now, 3600.) + 3600.;	1785	return now + (3600. - fmod (now, 3600.));
1293	}	1786	}
1294		1787
1295	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);	1788	ev_periodic_init (&hourly_tick, clock_cb, 0., 0., my_scheduler_cb);
1296		1789
1297	Example: Call a callback every hour, starting now:	1790	Example: Call a callback every hour, starting now:
1298		1791
1299	struct ev_periodic hourly_tick;	1792	ev_periodic hourly_tick;
1300	ev_periodic_init (&hourly_tick, clock_cb,	1793	ev_periodic_init (&hourly_tick, clock_cb,
1301	fmod (ev_now (loop), 3600.), 3600., 0);	1794	fmod (ev_now (loop), 3600.), 3600., 0);
1302	ev_periodic_start (loop, &hourly_tick);	1795	ev_periodic_start (loop, &hourly_tick);
1303		1796
1304		1797
1305	=head2 C<ev_signal> - signal me when a signal gets signalled!	1798	=head2 C<ev_signal> - signal me when a signal gets signalled!
1306		1799
1307	Signal watchers will trigger an event when the process receives a specific	1800	Signal watchers will trigger an event when the process receives a specific
1308	signal one or more times. Even though signals are very asynchronous, libev	1801	signal one or more times. Even though signals are very asynchronous, libev
1309	will try it's best to deliver signals synchronously, i.e. as part of the	1802	will try it's best to deliver signals synchronously, i.e. as part of the
1310	normal event processing, like any other event.	1803	normal event processing, like any other event.
1311		1804
		1805	If you want signals asynchronously, just use C<sigaction> as you would
		1806	do without libev and forget about sharing the signal. You can even use
		1807	C<ev_async> from a signal handler to synchronously wake up an event loop.
		1808
1312	You can configure as many watchers as you like per signal. Only when the	1809	You can configure as many watchers as you like per signal. Only when the
1313	first watcher gets started will libev actually register a signal watcher	1810	first watcher gets started will libev actually register a signal handler
1314	with the kernel (thus it coexists with your own signal handlers as long	1811	with the kernel (thus it coexists with your own signal handlers as long as
1315	as you don't register any with libev). Similarly, when the last signal	1812	you don't register any with libev for the same signal). Similarly, when
1316	watcher for a signal is stopped libev will reset the signal handler to	1813	the last signal watcher for a signal is stopped, libev will reset the
1317	SIG_DFL (regardless of what it was set to before).	1814	signal handler to SIG_DFL (regardless of what it was set to before).
		1815
		1816	If possible and supported, libev will install its handlers with
		1817	C<SA_RESTART> behaviour enabled, so system calls should not be unduly
		1818	interrupted. If you have a problem with system calls getting interrupted by
		1819	signals you can block all signals in an C<ev_check> watcher and unblock
		1820	them in an C<ev_prepare> watcher.
1318		1821
1319	=head3 Watcher-Specific Functions and Data Members	1822	=head3 Watcher-Specific Functions and Data Members
1320		1823
1321	=over 4	1824	=over 4
1322		1825
…		…
1331		1834
1332	The signal the watcher watches out for.	1835	The signal the watcher watches out for.
1333		1836
1334	=back	1837	=back
1335		1838
		1839	=head3 Examples
		1840
		1841	Example: Try to exit cleanly on SIGINT.
		1842
		1843	static void
		1844	sigint_cb (struct ev_loop *loop, ev_signal *w, int revents)
		1845	{
		1846	ev_unloop (loop, EVUNLOOP_ALL);
		1847	}
		1848
		1849	ev_signal signal_watcher;
		1850	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);
		1851	ev_signal_start (loop, &signal_watcher);
		1852
1336		1853
1337	=head2 C<ev_child> - watch out for process status changes	1854	=head2 C<ev_child> - watch out for process status changes
1338		1855
1339	Child watchers trigger when your process receives a SIGCHLD in response to	1856	Child watchers trigger when your process receives a SIGCHLD in response to
1340	some child status changes (most typically when a child of yours dies).	1857	some child status changes (most typically when a child of yours dies or
		1858	exits). It is permissible to install a child watcher I<after> the child
		1859	has been forked (which implies it might have already exited), as long
		1860	as the event loop isn't entered (or is continued from a watcher), i.e.,
		1861	forking and then immediately registering a watcher for the child is fine,
		1862	but forking and registering a watcher a few event loop iterations later is
		1863	not.
		1864
		1865	Only the default event loop is capable of handling signals, and therefore
		1866	you can only register child watchers in the default event loop.
		1867
		1868	=head3 Process Interaction
		1869
		1870	Libev grabs C<SIGCHLD> as soon as the default event loop is
		1871	initialised. This is necessary to guarantee proper behaviour even if
		1872	the first child watcher is started after the child exits. The occurrence
		1873	of C<SIGCHLD> is recorded asynchronously, but child reaping is done
		1874	synchronously as part of the event loop processing. Libev always reaps all
		1875	children, even ones not watched.
		1876
		1877	=head3 Overriding the Built-In Processing
		1878
		1879	Libev offers no special support for overriding the built-in child
		1880	processing, but if your application collides with libev's default child
		1881	handler, you can override it easily by installing your own handler for
		1882	C<SIGCHLD> after initialising the default loop, and making sure the
		1883	default loop never gets destroyed. You are encouraged, however, to use an
		1884	event-based approach to child reaping and thus use libev's support for
		1885	that, so other libev users can use C<ev_child> watchers freely.
		1886
		1887	=head3 Stopping the Child Watcher
		1888
		1889	Currently, the child watcher never gets stopped, even when the
		1890	child terminates, so normally one needs to stop the watcher in the
		1891	callback. Future versions of libev might stop the watcher automatically
		1892	when a child exit is detected.
1341		1893
1342	=head3 Watcher-Specific Functions and Data Members	1894	=head3 Watcher-Specific Functions and Data Members
1343		1895
1344	=over 4	1896	=over 4
1345		1897
1346	=item ev_child_init (ev_child *, callback, int pid)	1898	=item ev_child_init (ev_child *, callback, int pid, int trace)
1347		1899
1348	=item ev_child_set (ev_child *, int pid)	1900	=item ev_child_set (ev_child *, int pid, int trace)
1349		1901
1350	Configures the watcher to wait for status changes of process C<pid> (or	1902	Configures the watcher to wait for status changes of process C<pid> (or
1351	I<any> process if C<pid> is specified as C<0>). The callback can look	1903	I<any> process if C<pid> is specified as C<0>). The callback can look
1352	at the C<rstatus> member of the C<ev_child> watcher structure to see	1904	at the C<rstatus> member of the C<ev_child> watcher structure to see
1353	the status word (use the macros from C<sys/wait.h> and see your systems	1905	the status word (use the macros from C<sys/wait.h> and see your systems
1354	C<waitpid> documentation). The C<rpid> member contains the pid of the	1906	C<waitpid> documentation). The C<rpid> member contains the pid of the
1355	process causing the status change.	1907	process causing the status change. C<trace> must be either C<0> (only
		1908	activate the watcher when the process terminates) or C<1> (additionally
		1909	activate the watcher when the process is stopped or continued).
1356		1910
1357	=item int pid [read-only]	1911	=item int pid [read-only]
1358		1912
1359	The process id this watcher watches out for, or C<0>, meaning any process id.	1913	The process id this watcher watches out for, or C<0>, meaning any process id.
1360		1914
…		…
1367	The process exit/trace status caused by C<rpid> (see your systems	1921	The process exit/trace status caused by C<rpid> (see your systems
1368	C<waitpid> and C<sys/wait.h> documentation for details).	1922	C<waitpid> and C<sys/wait.h> documentation for details).
1369		1923
1370	=back	1924	=back
1371		1925
1372	Example: Try to exit cleanly on SIGINT and SIGTERM.	1926	=head3 Examples
1373		1927
		1928	Example: C<fork()> a new process and install a child handler to wait for
		1929	its completion.
		1930
		1931	ev_child cw;
		1932
1374	static void	1933	static void
1375	sigint_cb (struct ev_loop *loop, struct ev_signal *w, int revents)	1934	child_cb (EV_P_ ev_child *w, int revents)
1376	{	1935	{
1377	ev_unloop (loop, EVUNLOOP_ALL);	1936	ev_child_stop (EV_A_ w);
		1937	printf ("process %d exited with status %x\n", w->rpid, w->rstatus);
1378	}	1938	}
1379		1939
1380	struct ev_signal signal_watcher;	1940	pid_t pid = fork ();
1381	ev_signal_init (&signal_watcher, sigint_cb, SIGINT);	1941
1382	ev_signal_start (loop, &sigint_cb);	1942	if (pid < 0)
		1943	// error
		1944	else if (pid == 0)
		1945	{
		1946	// the forked child executes here
		1947	exit (1);
		1948	}
		1949	else
		1950	{
		1951	ev_child_init (&cw, child_cb, pid, 0);
		1952	ev_child_start (EV_DEFAULT_ &cw);
		1953	}
1383		1954
1384		1955
1385	=head2 C<ev_stat> - did the file attributes just change?	1956	=head2 C<ev_stat> - did the file attributes just change?
1386		1957
1387	This watches a filesystem path for attribute changes. That is, it calls	1958	This watches a file system path for attribute changes. That is, it calls
1388	C<stat> regularly (or when the OS says it changed) and sees if it changed	1959	C<stat> on that path in regular intervals (or when the OS says it changed)
1389	compared to the last time, invoking the callback if it did.	1960	and sees if it changed compared to the last time, invoking the callback if
		1961	it did.
1390		1962
1391	The path does not need to exist: changing from "path exists" to "path does	1963	The path does not need to exist: changing from "path exists" to "path does
1392	not exist" is a status change like any other. The condition "path does	1964	not exist" is a status change like any other. The condition "path does not
1393	not exist" is signified by the C<st_nlink> field being zero (which is	1965	exist" (or more correctly "path cannot be stat'ed") is signified by the
1394	otherwise always forced to be at least one) and all the other fields of	1966	C<st_nlink> field being zero (which is otherwise always forced to be at
1395	the stat buffer having unspecified contents.	1967	least one) and all the other fields of the stat buffer having unspecified
		1968	contents.
1396		1969
1397	The path I<should> be absolute and I<must not> end in a slash. If it is	1970	The path I<must not> end in a slash or contain special components such as
		1971	C<.> or C<..>. The path I<should> be absolute: If it is relative and
1398	relative and your working directory changes, the behaviour is undefined.	1972	your working directory changes, then the behaviour is undefined.
1399		1973
1400	Since there is no standard to do this, the portable implementation simply	1974	Since there is no portable change notification interface available, the
1401	calls C<stat (2)> regularly on the path to see if it changed somehow. You	1975	portable implementation simply calls C<stat(2)> regularly on the path
1402	can specify a recommended polling interval for this case. If you specify	1976	to see if it changed somehow. You can specify a recommended polling
1403	a polling interval of C<0> (highly recommended!) then a I<suitable,	1977	interval for this case. If you specify a polling interval of C<0> (highly
1404	unspecified default> value will be used (which you can expect to be around	1978	recommended!) then a I<suitable, unspecified default> value will be used
1405	five seconds, although this might change dynamically). Libev will also	1979	(which you can expect to be around five seconds, although this might
1406	impose a minimum interval which is currently around C<0.1>, but thats	1980	change dynamically). Libev will also impose a minimum interval which is
1407	usually overkill.	1981	currently around C<0.1>, but that's usually overkill.
1408		1982
1409	This watcher type is not meant for massive numbers of stat watchers,	1983	This watcher type is not meant for massive numbers of stat watchers,
1410	as even with OS-supported change notifications, this can be	1984	as even with OS-supported change notifications, this can be
1411	resource-intensive.	1985	resource-intensive.
1412		1986
1413	At the time of this writing, only the Linux inotify interface is	1987	At the time of this writing, the only OS-specific interface implemented
1414	implemented (implementing kqueue support is left as an exercise for the	1988	is the Linux inotify interface (implementing kqueue support is left as an
1415	reader). Inotify will be used to give hints only and should not change the	1989	exercise for the reader. Note, however, that the author sees no way of
1416	semantics of C<ev_stat> watchers, which means that libev sometimes needs	1990	implementing C<ev_stat> semantics with kqueue, except as a hint).
1417	to fall back to regular polling again even with inotify, but changes are	1991
1418	usually detected immediately, and if the file exists there will be no	1992	=head3 ABI Issues (Largefile Support)
1419	polling.	1993
		1994	Libev by default (unless the user overrides this) uses the default
		1995	compilation environment, which means that on systems with large file
		1996	support disabled by default, you get the 32 bit version of the stat
		1997	structure. When using the library from programs that change the ABI to
		1998	use 64 bit file offsets the programs will fail. In that case you have to
		1999	compile libev with the same flags to get binary compatibility. This is
		2000	obviously the case with any flags that change the ABI, but the problem is
		2001	most noticeably displayed with ev_stat and large file support.
		2002
		2003	The solution for this is to lobby your distribution maker to make large
		2004	file interfaces available by default (as e.g. FreeBSD does) and not
		2005	optional. Libev cannot simply switch on large file support because it has
		2006	to exchange stat structures with application programs compiled using the
		2007	default compilation environment.
		2008
		2009	=head3 Inotify and Kqueue
		2010
		2011	When C<inotify (7)> support has been compiled into libev and present at
		2012	runtime, it will be used to speed up change detection where possible. The
		2013	inotify descriptor will be created lazily when the first C<ev_stat>
		2014	watcher is being started.
		2015
		2016	Inotify presence does not change the semantics of C<ev_stat> watchers
		2017	except that changes might be detected earlier, and in some cases, to avoid
		2018	making regular C<stat> calls. Even in the presence of inotify support
		2019	there are many cases where libev has to resort to regular C<stat> polling,
		2020	but as long as kernel 2.6.25 or newer is used (2.6.24 and older have too
		2021	many bugs), the path exists (i.e. stat succeeds), and the path resides on
		2022	a local filesystem (libev currently assumes only ext2/3, jfs, reiserfs and
		2023	xfs are fully working) libev usually gets away without polling.
		2024
		2025	There is no support for kqueue, as apparently it cannot be used to
		2026	implement this functionality, due to the requirement of having a file
		2027	descriptor open on the object at all times, and detecting renames, unlinks
		2028	etc. is difficult.
		2029
		2030	=head3 C<stat ()> is a synchronous operation
		2031
		2032	Libev doesn't normally do any kind of I/O itself, and so is not blocking
		2033	the process. The exception are C<ev_stat> watchers - those call C<stat
		2034	()>, which is a synchronous operation.
		2035
		2036	For local paths, this usually doesn't matter: unless the system is very
		2037	busy or the intervals between stat's are large, a stat call will be fast,
		2038	as the path data is usually in memory already (except when starting the
		2039	watcher).
		2040
		2041	For networked file systems, calling C<stat ()> can block an indefinite
		2042	time due to network issues, and even under good conditions, a stat call
		2043	often takes multiple milliseconds.
		2044
		2045	Therefore, it is best to avoid using C<ev_stat> watchers on networked
		2046	paths, although this is fully supported by libev.
		2047
		2048	=head3 The special problem of stat time resolution
		2049
		2050	The C<stat ()> system call only supports full-second resolution portably,
		2051	and even on systems where the resolution is higher, most file systems
		2052	still only support whole seconds.
		2053
		2054	That means that, if the time is the only thing that changes, you can
		2055	easily miss updates: on the first update, C<ev_stat> detects a change and
		2056	calls your callback, which does something. When there is another update
		2057	within the same second, C<ev_stat> will be unable to detect unless the
		2058	stat data does change in other ways (e.g. file size).
		2059
		2060	The solution to this is to delay acting on a change for slightly more
		2061	than a second (or till slightly after the next full second boundary), using
		2062	a roughly one-second-delay C<ev_timer> (e.g. C<ev_timer_set (w, 0., 1.02);
		2063	ev_timer_again (loop, w)>).
		2064
		2065	The C<.02> offset is added to work around small timing inconsistencies
		2066	of some operating systems (where the second counter of the current time
		2067	might be be delayed. One such system is the Linux kernel, where a call to
		2068	C<gettimeofday> might return a timestamp with a full second later than
		2069	a subsequent C<time> call - if the equivalent of C<time ()> is used to
		2070	update file times then there will be a small window where the kernel uses
		2071	the previous second to update file times but libev might already execute
		2072	the timer callback).
1420		2073
1421	=head3 Watcher-Specific Functions and Data Members	2074	=head3 Watcher-Specific Functions and Data Members
1422		2075
1423	=over 4	2076	=over 4
1424		2077
…		…
1430	C<path>. The C<interval> is a hint on how quickly a change is expected to	2083	C<path>. The C<interval> is a hint on how quickly a change is expected to
1431	be detected and should normally be specified as C<0> to let libev choose	2084	be detected and should normally be specified as C<0> to let libev choose
1432	a suitable value. The memory pointed to by C<path> must point to the same	2085	a suitable value. The memory pointed to by C<path> must point to the same
1433	path for as long as the watcher is active.	2086	path for as long as the watcher is active.
1434		2087
1435	The callback will be receive C<EV_STAT> when a change was detected,	2088	The callback will receive an C<EV_STAT> event when a change was detected,
1436	relative to the attributes at the time the watcher was started (or the	2089	relative to the attributes at the time the watcher was started (or the
1437	last change was detected).	2090	last change was detected).
1438		2091
1439	=item ev_stat_stat (ev_stat *)	2092	=item ev_stat_stat (loop, ev_stat *)
1440		2093
1441	Updates the stat buffer immediately with new values. If you change the	2094	Updates the stat buffer immediately with new values. If you change the
1442	watched path in your callback, you could call this fucntion to avoid	2095	watched path in your callback, you could call this function to avoid
1443	detecting this change (while introducing a race condition). Can also be	2096	detecting this change (while introducing a race condition if you are not
1444	useful simply to find out the new values.	2097	the only one changing the path). Can also be useful simply to find out the
		2098	new values.
1445		2099
1446	=item ev_statdata attr [read-only]	2100	=item ev_statdata attr [read-only]
1447		2101
1448	The most-recently detected attributes of the file. Although the type is of	2102	The most-recently detected attributes of the file. Although the type is
1449	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types	2103	C<ev_statdata>, this is usually the (or one of the) C<struct stat> types
1450	suitable for your system. If the C<st_nlink> member is C<0>, then there	2104	suitable for your system, but you can only rely on the POSIX-standardised
		2105	members to be present. If the C<st_nlink> member is C<0>, then there was
1451	was some error while C<stat>ing the file.	2106	some error while C<stat>ing the file.
1452		2107
1453	=item ev_statdata prev [read-only]	2108	=item ev_statdata prev [read-only]
1454		2109
1455	The previous attributes of the file. The callback gets invoked whenever	2110	The previous attributes of the file. The callback gets invoked whenever
1456	C<prev> != C<attr>.	2111	C<prev> != C<attr>, or, more precisely, one or more of these members
		2112	differ: C<st_dev>, C<st_ino>, C<st_mode>, C<st_nlink>, C<st_uid>,
		2113	C<st_gid>, C<st_rdev>, C<st_size>, C<st_atime>, C<st_mtime>, C<st_ctime>.
1457		2114
1458	=item ev_tstamp interval [read-only]	2115	=item ev_tstamp interval [read-only]
1459		2116
1460	The specified interval.	2117	The specified interval.
1461		2118
1462	=item const char *path [read-only]	2119	=item const char *path [read-only]
1463		2120
1464	The filesystem path that is being watched.	2121	The file system path that is being watched.
1465		2122
1466	=back	2123	=back
1467		2124
		2125	=head3 Examples
		2126
1468	Example: Watch C</etc/passwd> for attribute changes.	2127	Example: Watch C</etc/passwd> for attribute changes.
1469		2128
1470	static void	2129	static void
1471	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)	2130	passwd_cb (struct ev_loop *loop, ev_stat *w, int revents)
1472	{	2131	{
1473	/* /etc/passwd changed in some way */	2132	/* /etc/passwd changed in some way */
1474	if (w->attr.st_nlink)	2133	if (w->attr.st_nlink)
1475	{	2134	{
1476	printf ("passwd current size %ld\n", (long)w->attr.st_size);	2135	printf ("passwd current size %ld\n", (long)w->attr.st_size);
1477	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);	2136	printf ("passwd current atime %ld\n", (long)w->attr.st_mtime);
1478	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);	2137	printf ("passwd current mtime %ld\n", (long)w->attr.st_mtime);
1479	}	2138	}
1480	else	2139	else
1481	/* you shalt not abuse printf for puts */	2140	/* you shalt not abuse printf for puts */
1482	puts ("wow, /etc/passwd is not there, expect problems. "	2141	puts ("wow, /etc/passwd is not there, expect problems. "
1483	"if this is windows, they already arrived\n");	2142	"if this is windows, they already arrived\n");
1484	}	2143	}
1485		2144
1486	...	2145	...
1487	ev_stat passwd;	2146	ev_stat passwd;
1488		2147
1489	ev_stat_init (&passwd, passwd_cb, "/etc/passwd");	2148	ev_stat_init (&passwd, passwd_cb, "/etc/passwd", 0.);
1490	ev_stat_start (loop, &passwd);	2149	ev_stat_start (loop, &passwd);
		2150
		2151	Example: Like above, but additionally use a one-second delay so we do not
		2152	miss updates (however, frequent updates will delay processing, too, so
		2153	one might do the work both on C<ev_stat> callback invocation I<and> on
		2154	C<ev_timer> callback invocation).
		2155
		2156	static ev_stat passwd;
		2157	static ev_timer timer;
		2158
		2159	static void
		2160	timer_cb (EV_P_ ev_timer *w, int revents)
		2161	{
		2162	ev_timer_stop (EV_A_ w);
		2163
		2164	/* now it's one second after the most recent passwd change */
		2165	}
		2166
		2167	static void
		2168	stat_cb (EV_P_ ev_stat *w, int revents)
		2169	{
		2170	/* reset the one-second timer */
		2171	ev_timer_again (EV_A_ &timer);
		2172	}
		2173
		2174	...
		2175	ev_stat_init (&passwd, stat_cb, "/etc/passwd", 0.);
		2176	ev_stat_start (loop, &passwd);
		2177	ev_timer_init (&timer, timer_cb, 0., 1.02);
1491		2178
1492		2179
1493	=head2 C<ev_idle> - when you've got nothing better to do...	2180	=head2 C<ev_idle> - when you've got nothing better to do...
1494		2181
1495	Idle watchers trigger events when no other events of the same or higher	2182	Idle watchers trigger events when no other events of the same or higher
1496	priority are pending (prepare, check and other idle watchers do not	2183	priority are pending (prepare, check and other idle watchers do not count
1497	count).	2184	as receiving "events").
1498		2185
1499	That is, as long as your process is busy handling sockets or timeouts	2186	That is, as long as your process is busy handling sockets or timeouts
1500	(or even signals, imagine) of the same or higher priority it will not be	2187	(or even signals, imagine) of the same or higher priority it will not be
1501	triggered. But when your process is idle (or only lower-priority watchers	2188	triggered. But when your process is idle (or only lower-priority watchers
1502	are pending), the idle watchers are being called once per event loop	2189	are pending), the idle watchers are being called once per event loop
…		…
1513		2200
1514	=head3 Watcher-Specific Functions and Data Members	2201	=head3 Watcher-Specific Functions and Data Members
1515		2202
1516	=over 4	2203	=over 4
1517		2204
1518	=item ev_idle_init (ev_signal *, callback)	2205	=item ev_idle_init (ev_idle *, callback)
1519		2206
1520	Initialises and configures the idle watcher - it has no parameters of any	2207	Initialises and configures the idle watcher - it has no parameters of any
1521	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,	2208	kind. There is a C<ev_idle_set> macro, but using it is utterly pointless,
1522	believe me.	2209	believe me.
1523		2210
1524	=back	2211	=back
1525		2212
		2213	=head3 Examples
		2214
1526	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the	2215	Example: Dynamically allocate an C<ev_idle> watcher, start it, and in the
1527	callback, free it. Also, use no error checking, as usual.	2216	callback, free it. Also, use no error checking, as usual.
1528		2217
1529	static void	2218	static void
1530	idle_cb (struct ev_loop *loop, struct ev_idle *w, int revents)	2219	idle_cb (struct ev_loop *loop, ev_idle *w, int revents)
1531	{	2220	{
1532	free (w);	2221	free (w);
1533	// now do something you wanted to do when the program has	2222	// now do something you wanted to do when the program has
1534	// no longer asnything immediate to do.	2223	// no longer anything immediate to do.
1535	}	2224	}
1536		2225
1537	struct ev_idle *idle_watcher = malloc (sizeof (struct ev_idle));	2226	ev_idle *idle_watcher = malloc (sizeof (ev_idle));
1538	ev_idle_init (idle_watcher, idle_cb);	2227	ev_idle_init (idle_watcher, idle_cb);
1539	ev_idle_start (loop, idle_cb);	2228	ev_idle_start (loop, idle_cb);
1540		2229
1541		2230
1542	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!	2231	=head2 C<ev_prepare> and C<ev_check> - customise your event loop!
1543		2232
1544	Prepare and check watchers are usually (but not always) used in tandem:	2233	Prepare and check watchers are usually (but not always) used in pairs:
1545	prepare watchers get invoked before the process blocks and check watchers	2234	prepare watchers get invoked before the process blocks and check watchers
1546	afterwards.	2235	afterwards.
1547		2236
1548	You I<must not> call C<ev_loop> or similar functions that enter	2237	You I<must not> call C<ev_loop> or similar functions that enter
1549	the current event loop from either C<ev_prepare> or C<ev_check>	2238	the current event loop from either C<ev_prepare> or C<ev_check>
…		…
1552	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,	2241	those watchers, i.e. the sequence will always be C<ev_prepare>, blocking,
1553	C<ev_check> so if you have one watcher of each kind they will always be	2242	C<ev_check> so if you have one watcher of each kind they will always be
1554	called in pairs bracketing the blocking call.	2243	called in pairs bracketing the blocking call.
1555		2244
1556	Their main purpose is to integrate other event mechanisms into libev and	2245	Their main purpose is to integrate other event mechanisms into libev and
1557	their use is somewhat advanced. This could be used, for example, to track	2246	their use is somewhat advanced. They could be used, for example, to track
1558	variable changes, implement your own watchers, integrate net-snmp or a	2247	variable changes, implement your own watchers, integrate net-snmp or a
1559	coroutine library and lots more. They are also occasionally useful if	2248	coroutine library and lots more. They are also occasionally useful if
1560	you cache some data and want to flush it before blocking (for example,	2249	you cache some data and want to flush it before blocking (for example,
1561	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>	2250	in X programs you might want to do an C<XFlush ()> in an C<ev_prepare>
1562	watcher).	2251	watcher).
1563		2252
1564	This is done by examining in each prepare call which file descriptors need	2253	This is done by examining in each prepare call which file descriptors
1565	to be watched by the other library, registering C<ev_io> watchers for	2254	need to be watched by the other library, registering C<ev_io> watchers
1566	them and starting an C<ev_timer> watcher for any timeouts (many libraries	2255	for them and starting an C<ev_timer> watcher for any timeouts (many
1567	provide just this functionality). Then, in the check watcher you check for	2256	libraries provide exactly this functionality). Then, in the check watcher,
1568	any events that occured (by checking the pending status of all watchers	2257	you check for any events that occurred (by checking the pending status
1569	and stopping them) and call back into the library. The I/O and timer	2258	of all watchers and stopping them) and call back into the library. The
1570	callbacks will never actually be called (but must be valid nevertheless,	2259	I/O and timer callbacks will never actually be called (but must be valid
1571	because you never know, you know?).	2260	nevertheless, because you never know, you know?).
1572		2261
1573	As another example, the Perl Coro module uses these hooks to integrate	2262	As another example, the Perl Coro module uses these hooks to integrate
1574	coroutines into libev programs, by yielding to other active coroutines	2263	coroutines into libev programs, by yielding to other active coroutines
1575	during each prepare and only letting the process block if no coroutines	2264	during each prepare and only letting the process block if no coroutines
1576	are ready to run (it's actually more complicated: it only runs coroutines	2265	are ready to run (it's actually more complicated: it only runs coroutines
…		…
1579	loop from blocking if lower-priority coroutines are active, thus mapping	2268	loop from blocking if lower-priority coroutines are active, thus mapping
1580	low-priority coroutines to idle/background tasks).	2269	low-priority coroutines to idle/background tasks).
1581		2270
1582	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)	2271	It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1583	priority, to ensure that they are being run before any other watchers	2272	priority, to ensure that they are being run before any other watchers
		2273	after the poll (this doesn't matter for C<ev_prepare> watchers).
		2274
1584	after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,	2275	Also, C<ev_check> watchers (and C<ev_prepare> watchers, too) should not
1585	too) should not activate ("feed") events into libev. While libev fully	2276	activate ("feed") events into libev. While libev fully supports this, they
1586	supports this, they will be called before other C<ev_check> watchers did	2277	might get executed before other C<ev_check> watchers did their job. As
1587	their job. As C<ev_check> watchers are often used to embed other event	2278	C<ev_check> watchers are often used to embed other (non-libev) event
1588	loops those other event loops might be in an unusable state until their	2279	loops those other event loops might be in an unusable state until their
1589	C<ev_check> watcher ran (always remind yourself to coexist peacefully with	2280	C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1590	others).	2281	others).
1591		2282
1592	=head3 Watcher-Specific Functions and Data Members	2283	=head3 Watcher-Specific Functions and Data Members
…		…
1597		2288
1598	=item ev_check_init (ev_check *, callback)	2289	=item ev_check_init (ev_check *, callback)
1599		2290
1600	Initialises and configures the prepare or check watcher - they have no	2291	Initialises and configures the prepare or check watcher - they have no
1601	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>	2292	parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1602	macros, but using them is utterly, utterly and completely pointless.	2293	macros, but using them is utterly, utterly, utterly and completely
		2294	pointless.
1603		2295
1604	=back	2296	=back
		2297
		2298	=head3 Examples
1605		2299
1606	There are a number of principal ways to embed other event loops or modules	2300	There are a number of principal ways to embed other event loops or modules
1607	into libev. Here are some ideas on how to include libadns into libev	2301	into libev. Here are some ideas on how to include libadns into libev
1608	(there is a Perl module named C<EV::ADNS> that does this, which you could	2302	(there is a Perl module named C<EV::ADNS> that does this, which you could
1609	use for an actually working example. Another Perl module named C<EV::Glib>	2303	use as a working example. Another Perl module named C<EV::Glib> embeds a
1610	embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV	2304	Glib main context into libev, and finally, C<Glib::EV> embeds EV into the
1611	into the Glib event loop).	2305	Glib event loop).
1612		2306
1613	Method 1: Add IO watchers and a timeout watcher in a prepare handler,	2307	Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1614	and in a check watcher, destroy them and call into libadns. What follows	2308	and in a check watcher, destroy them and call into libadns. What follows
1615	is pseudo-code only of course. This requires you to either use a low	2309	is pseudo-code only of course. This requires you to either use a low
1616	priority for the check watcher or use C<ev_clear_pending> explicitly, as	2310	priority for the check watcher or use C<ev_clear_pending> explicitly, as
1617	the callbacks for the IO/timeout watchers might not have been called yet.	2311	the callbacks for the IO/timeout watchers might not have been called yet.
1618		2312
1619	static ev_io iow [nfd];	2313	static ev_io iow [nfd];
1620	static ev_timer tw;	2314	static ev_timer tw;
1621		2315
1622	static void	2316	static void
1623	io_cb (ev_loop *loop, ev_io *w, int revents)	2317	io_cb (struct ev_loop *loop, ev_io *w, int revents)
1624	{	2318	{
1625	}	2319	}
1626		2320
1627	// create io watchers for each fd and a timer before blocking	2321	// create io watchers for each fd and a timer before blocking
1628	static void	2322	static void
1629	adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)	2323	adns_prepare_cb (struct ev_loop *loop, ev_prepare *w, int revents)
1630	{	2324	{
1631	int timeout = 3600000;	2325	int timeout = 3600000;
1632	struct pollfd fds [nfd];	2326	struct pollfd fds [nfd];
1633	// actual code will need to loop here and realloc etc.	2327	// actual code will need to loop here and realloc etc.
1634	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));	2328	adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
1635		2329
1636	/* the callback is illegal, but won't be called as we stop during check */	2330	/* the callback is illegal, but won't be called as we stop during check */
1637	ev_timer_init (&tw, 0, timeout * 1e-3);	2331	ev_timer_init (&tw, 0, timeout * 1e-3);
1638	ev_timer_start (loop, &tw);	2332	ev_timer_start (loop, &tw);
1639		2333
1640	// create one ev_io per pollfd	2334	// create one ev_io per pollfd
1641	for (int i = 0; i < nfd; ++i)	2335	for (int i = 0; i < nfd; ++i)
1642	{	2336	{
1643	ev_io_init (iow + i, io_cb, fds [i].fd,	2337	ev_io_init (iow + i, io_cb, fds [i].fd,
1644	((fds [i].events & POLLIN ? EV_READ : 0)	2338	((fds [i].events & POLLIN ? EV_READ : 0)
1645	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));	2339	| (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1646		2340
1647	fds [i].revents = 0;	2341	fds [i].revents = 0;
1648	ev_io_start (loop, iow + i);	2342	ev_io_start (loop, iow + i);
1649	}	2343	}
1650	}	2344	}
1651		2345
1652	// stop all watchers after blocking	2346	// stop all watchers after blocking
1653	static void	2347	static void
1654	adns_check_cb (ev_loop *loop, ev_check *w, int revents)	2348	adns_check_cb (struct ev_loop *loop, ev_check *w, int revents)
1655	{	2349	{
1656	ev_timer_stop (loop, &tw);	2350	ev_timer_stop (loop, &tw);
1657		2351
1658	for (int i = 0; i < nfd; ++i)	2352	for (int i = 0; i < nfd; ++i)
1659	{	2353	{
1660	// set the relevant poll flags	2354	// set the relevant poll flags
1661	// could also call adns_processreadable etc. here	2355	// could also call adns_processreadable etc. here
1662	struct pollfd *fd = fds + i;	2356	struct pollfd *fd = fds + i;
1663	int revents = ev_clear_pending (iow + i);	2357	int revents = ev_clear_pending (iow + i);
1664	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;	2358	if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1665	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;	2359	if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1666		2360
1667	// now stop the watcher	2361	// now stop the watcher
1668	ev_io_stop (loop, iow + i);	2362	ev_io_stop (loop, iow + i);
1669	}	2363	}
1670		2364
1671	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));	2365	adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1672	}	2366	}
1673		2367
1674	Method 2: This would be just like method 1, but you run C<adns_afterpoll>	2368	Method 2: This would be just like method 1, but you run C<adns_afterpoll>
1675	in the prepare watcher and would dispose of the check watcher.	2369	in the prepare watcher and would dispose of the check watcher.
1676		2370
1677	Method 3: If the module to be embedded supports explicit event	2371	Method 3: If the module to be embedded supports explicit event
1678	notification (adns does), you can also make use of the actual watcher	2372	notification (libadns does), you can also make use of the actual watcher
1679	callbacks, and only destroy/create the watchers in the prepare watcher.	2373	callbacks, and only destroy/create the watchers in the prepare watcher.
1680		2374
1681	static void	2375	static void
1682	timer_cb (EV_P_ ev_timer *w, int revents)	2376	timer_cb (EV_P_ ev_timer *w, int revents)
1683	{	2377	{
1684	adns_state ads = (adns_state)w->data;	2378	adns_state ads = (adns_state)w->data;
1685	update_now (EV_A);	2379	update_now (EV_A);
1686		2380
1687	adns_processtimeouts (ads, &tv_now);	2381	adns_processtimeouts (ads, &tv_now);
1688	}	2382	}
1689		2383
1690	static void	2384	static void
1691	io_cb (EV_P_ ev_io *w, int revents)	2385	io_cb (EV_P_ ev_io *w, int revents)
1692	{	2386	{
1693	adns_state ads = (adns_state)w->data;	2387	adns_state ads = (adns_state)w->data;
1694	update_now (EV_A);	2388	update_now (EV_A);
1695		2389
1696	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);	2390	if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1697	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);	2391	if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1698	}	2392	}
1699		2393
1700	// do not ever call adns_afterpoll	2394	// do not ever call adns_afterpoll
1701		2395
1702	Method 4: Do not use a prepare or check watcher because the module you	2396	Method 4: Do not use a prepare or check watcher because the module you
1703	want to embed is too inflexible to support it. Instead, youc na override	2397	want to embed is not flexible enough to support it. Instead, you can
1704	their poll function. The drawback with this solution is that the main	2398	override their poll function. The drawback with this solution is that the
1705	loop is now no longer controllable by EV. The C<Glib::EV> module does	2399	main loop is now no longer controllable by EV. The C<Glib::EV> module uses
1706	this.	2400	this approach, effectively embedding EV as a client into the horrible
		2401	libglib event loop.
1707		2402
1708	static gint	2403	static gint
1709	event_poll_func (GPollFD *fds, guint nfds, gint timeout)	2404	event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1710	{	2405	{
1711	int got_events = 0;	2406	int got_events = 0;
1712		2407
1713	for (n = 0; n < nfds; ++n)	2408	for (n = 0; n < nfds; ++n)
1714	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events	2409	// create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1715		2410
1716	if (timeout >= 0)	2411	if (timeout >= 0)
1717	// create/start timer	2412	// create/start timer
1718		2413
1719	// poll	2414	// poll
1720	ev_loop (EV_A_ 0);	2415	ev_loop (EV_A_ 0);
1721		2416
1722	// stop timer again	2417	// stop timer again
1723	if (timeout >= 0)	2418	if (timeout >= 0)
1724	ev_timer_stop (EV_A_ &to);	2419	ev_timer_stop (EV_A_ &to);
1725		2420
1726	// stop io watchers again - their callbacks should have set	2421	// stop io watchers again - their callbacks should have set
1727	for (n = 0; n < nfds; ++n)	2422	for (n = 0; n < nfds; ++n)
1728	ev_io_stop (EV_A_ iow [n]);	2423	ev_io_stop (EV_A_ iow [n]);
1729		2424
1730	return got_events;	2425	return got_events;
1731	}	2426	}
1732		2427
1733		2428
1734	=head2 C<ev_embed> - when one backend isn't enough...	2429	=head2 C<ev_embed> - when one backend isn't enough...
1735		2430
1736	This is a rather advanced watcher type that lets you embed one event loop	2431	This is a rather advanced watcher type that lets you embed one event loop
1737	into another (currently only C<ev_io> events are supported in the embedded	2432	into another (currently only C<ev_io> events are supported in the embedded
1738	loop, other types of watchers might be handled in a delayed or incorrect	2433	loop, other types of watchers might be handled in a delayed or incorrect
1739	fashion and must not be used). (See portability notes, below).	2434	fashion and must not be used).
1740		2435
1741	There are primarily two reasons you would want that: work around bugs and	2436	There are primarily two reasons you would want that: work around bugs and
1742	prioritise I/O.	2437	prioritise I/O.
1743		2438
1744	As an example for a bug workaround, the kqueue backend might only support	2439	As an example for a bug workaround, the kqueue backend might only support
1745	sockets on some platform, so it is unusable as generic backend, but you	2440	sockets on some platform, so it is unusable as generic backend, but you
1746	still want to make use of it because you have many sockets and it scales	2441	still want to make use of it because you have many sockets and it scales
1747	so nicely. In this case, you would create a kqueue-based loop and embed it	2442	so nicely. In this case, you would create a kqueue-based loop and embed
1748	into your default loop (which might use e.g. poll). Overall operation will	2443	it into your default loop (which might use e.g. poll). Overall operation
1749	be a bit slower because first libev has to poll and then call kevent, but	2444	will be a bit slower because first libev has to call C<poll> and then
1750	at least you can use both at what they are best.	2445	C<kevent>, but at least you can use both mechanisms for what they are
		2446	best: C<kqueue> for scalable sockets and C<poll> if you want it to work :)
1751		2447
1752	As for prioritising I/O: rarely you have the case where some fds have	2448	As for prioritising I/O: under rare circumstances you have the case where
1753	to be watched and handled very quickly (with low latency), and even	2449	some fds have to be watched and handled very quickly (with low latency),
1754	priorities and idle watchers might have too much overhead. In this case	2450	and even priorities and idle watchers might have too much overhead. In
1755	you would put all the high priority stuff in one loop and all the rest in	2451	this case you would put all the high priority stuff in one loop and all
1756	a second one, and embed the second one in the first.	2452	the rest in a second one, and embed the second one in the first.
1757		2453
1758	As long as the watcher is active, the callback will be invoked every time	2454	As long as the watcher is active, the callback will be invoked every
1759	there might be events pending in the embedded loop. The callback must then	2455	time there might be events pending in the embedded loop. The callback
1760	call C<ev_embed_sweep (mainloop, watcher)> to make a single sweep and invoke	2456	must then call C<ev_embed_sweep (mainloop, watcher)> to make a single
1761	their callbacks (you could also start an idle watcher to give the embedded	2457	sweep and invoke their callbacks (the callback doesn't need to invoke the
1762	loop strictly lower priority for example). You can also set the callback	2458	C<ev_embed_sweep> function directly, it could also start an idle watcher
1763	to C<0>, in which case the embed watcher will automatically execute the	2459	to give the embedded loop strictly lower priority for example).
1764	embedded loop sweep.
1765		2460
1766	As long as the watcher is started it will automatically handle events. The	2461	You can also set the callback to C<0>, in which case the embed watcher
1767	callback will be invoked whenever some events have been handled. You can	2462	will automatically execute the embedded loop sweep whenever necessary.
1768	set the callback to C<0> to avoid having to specify one if you are not
1769	interested in that.
1770		2463
1771	Also, there have not currently been made special provisions for forking:	2464	Fork detection will be handled transparently while the C<ev_embed> watcher
1772	when you fork, you not only have to call C<ev_loop_fork> on both loops,	2465	is active, i.e., the embedded loop will automatically be forked when the
1773	but you will also have to stop and restart any C<ev_embed> watchers	2466	embedding loop forks. In other cases, the user is responsible for calling
1774	yourself.	2467	C<ev_loop_fork> on the embedded loop.
1775		2468
1776	Unfortunately, not all backends are embeddable, only the ones returned by	2469	Unfortunately, not all backends are embeddable: only the ones returned by
1777	C<ev_embeddable_backends> are, which, unfortunately, does not include any	2470	C<ev_embeddable_backends> are, which, unfortunately, does not include any
1778	portable one.	2471	portable one.
1779		2472
1780	So when you want to use this feature you will always have to be prepared	2473	So when you want to use this feature you will always have to be prepared
1781	that you cannot get an embeddable loop. The recommended way to get around	2474	that you cannot get an embeddable loop. The recommended way to get around
1782	this is to have a separate variables for your embeddable loop, try to	2475	this is to have a separate variables for your embeddable loop, try to
1783	create it, and if that fails, use the normal loop for everything:	2476	create it, and if that fails, use the normal loop for everything.
1784		2477
1785	struct ev_loop *loop_hi = ev_default_init (0);	2478	=head3 C<ev_embed> and fork
1786	struct ev_loop *loop_lo = 0;
1787	struct ev_embed embed;
1788
1789	// see if there is a chance of getting one that works
1790	// (remember that a flags value of 0 means autodetection)
1791	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1792	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1793	: 0;
1794		2479
1795	// if we got one, then embed it, otherwise default to loop_hi	2480	While the C<ev_embed> watcher is running, forks in the embedding loop will
1796	if (loop_lo)	2481	automatically be applied to the embedded loop as well, so no special
1797	{	2482	fork handling is required in that case. When the watcher is not running,
1798	ev_embed_init (&embed, 0, loop_lo);	2483	however, it is still the task of the libev user to call C<ev_loop_fork ()>
1799	ev_embed_start (loop_hi, &embed);	2484	as applicable.
1800	}
1801	else
1802	loop_lo = loop_hi;
1803
1804	=head2 Portability notes
1805
1806	Kqueue is nominally embeddable, but this is broken on all BSDs that I
1807	tried, in various ways. Usually the embedded event loop will simply never
1808	receive events, sometimes it will only trigger a few times, sometimes in a
1809	loop. Epoll is also nominally embeddable, but many Linux kernel versions
1810	will always eport the epoll fd as ready, even when no events are pending.
1811
1812	While libev allows embedding these backends (they are contained in
1813	C<ev_embeddable_backends ()>), take extreme care that it will actually
1814	work.
1815
1816	When in doubt, create a dynamic event loop forced to use sockets (this
1817	usually works) and possibly another thread and a pipe or so to report to
1818	your main event loop.
1819		2485
1820	=head3 Watcher-Specific Functions and Data Members	2486	=head3 Watcher-Specific Functions and Data Members
1821		2487
1822	=over 4	2488	=over 4
1823		2489
…		…
1827		2493
1828	Configures the watcher to embed the given loop, which must be	2494	Configures the watcher to embed the given loop, which must be
1829	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be	2495	embeddable. If the callback is C<0>, then C<ev_embed_sweep> will be
1830	invoked automatically, otherwise it is the responsibility of the callback	2496	invoked automatically, otherwise it is the responsibility of the callback
1831	to invoke it (it will continue to be called until the sweep has been done,	2497	to invoke it (it will continue to be called until the sweep has been done,
1832	if you do not want thta, you need to temporarily stop the embed watcher).	2498	if you do not want that, you need to temporarily stop the embed watcher).
1833		2499
1834	=item ev_embed_sweep (loop, ev_embed *)	2500	=item ev_embed_sweep (loop, ev_embed *)
1835		2501
1836	Make a single, non-blocking sweep over the embedded loop. This works	2502	Make a single, non-blocking sweep over the embedded loop. This works
1837	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most	2503	similarly to C<ev_loop (embedded_loop, EVLOOP_NONBLOCK)>, but in the most
1838	apropriate way for embedded loops.	2504	appropriate way for embedded loops.
1839		2505
1840	=item struct ev_loop *other [read-only]	2506	=item struct ev_loop *other [read-only]
1841		2507
1842	The embedded event loop.	2508	The embedded event loop.
1843		2509
1844	=back	2510	=back
		2511
		2512	=head3 Examples
		2513
		2514	Example: Try to get an embeddable event loop and embed it into the default
		2515	event loop. If that is not possible, use the default loop. The default
		2516	loop is stored in C<loop_hi>, while the embeddable loop is stored in
		2517	C<loop_lo> (which is C<loop_hi> in the case no embeddable loop can be
		2518	used).
		2519
		2520	struct ev_loop *loop_hi = ev_default_init (0);
		2521	struct ev_loop *loop_lo = 0;
		2522	ev_embed embed;
		2523
		2524	// see if there is a chance of getting one that works
		2525	// (remember that a flags value of 0 means autodetection)
		2526	loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
		2527	? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
		2528	: 0;
		2529
		2530	// if we got one, then embed it, otherwise default to loop_hi
		2531	if (loop_lo)
		2532	{
		2533	ev_embed_init (&embed, 0, loop_lo);
		2534	ev_embed_start (loop_hi, &embed);
		2535	}
		2536	else
		2537	loop_lo = loop_hi;
		2538
		2539	Example: Check if kqueue is available but not recommended and create
		2540	a kqueue backend for use with sockets (which usually work with any
		2541	kqueue implementation). Store the kqueue/socket-only event loop in
		2542	C<loop_socket>. (One might optionally use C<EVFLAG_NOENV>, too).
		2543
		2544	struct ev_loop *loop = ev_default_init (0);
		2545	struct ev_loop *loop_socket = 0;
		2546	ev_embed embed;
		2547
		2548	if (ev_supported_backends () & ~ev_recommended_backends () & EVBACKEND_KQUEUE)
		2549	if ((loop_socket = ev_loop_new (EVBACKEND_KQUEUE))
		2550	{
		2551	ev_embed_init (&embed, 0, loop_socket);
		2552	ev_embed_start (loop, &embed);
		2553	}
		2554
		2555	if (!loop_socket)
		2556	loop_socket = loop;
		2557
		2558	// now use loop_socket for all sockets, and loop for everything else
1845		2559
1846		2560
1847	=head2 C<ev_fork> - the audacity to resume the event loop after a fork	2561	=head2 C<ev_fork> - the audacity to resume the event loop after a fork
1848		2562
1849	Fork watchers are called when a C<fork ()> was detected (usually because	2563	Fork watchers are called when a C<fork ()> was detected (usually because
…		…
1865	believe me.	2579	believe me.
1866		2580
1867	=back	2581	=back
1868		2582
1869		2583
		2584	=head2 C<ev_async> - how to wake up another event loop
		2585
		2586	In general, you cannot use an C<ev_loop> from multiple threads or other
		2587	asynchronous sources such as signal handlers (as opposed to multiple event
		2588	loops - those are of course safe to use in different threads).
		2589
		2590	Sometimes, however, you need to wake up another event loop you do not
		2591	control, for example because it belongs to another thread. This is what
		2592	C<ev_async> watchers do: as long as the C<ev_async> watcher is active, you
		2593	can signal it by calling C<ev_async_send>, which is thread- and signal
		2594	safe.
		2595
		2596	This functionality is very similar to C<ev_signal> watchers, as signals,
		2597	too, are asynchronous in nature, and signals, too, will be compressed
		2598	(i.e. the number of callback invocations may be less than the number of
		2599	C<ev_async_sent> calls).
		2600
		2601	Unlike C<ev_signal> watchers, C<ev_async> works with any event loop, not
		2602	just the default loop.
		2603
		2604	=head3 Queueing
		2605
		2606	C<ev_async> does not support queueing of data in any way. The reason
		2607	is that the author does not know of a simple (or any) algorithm for a
		2608	multiple-writer-single-reader queue that works in all cases and doesn't
		2609	need elaborate support such as pthreads.
		2610
		2611	That means that if you want to queue data, you have to provide your own
		2612	queue. But at least I can tell you how to implement locking around your
		2613	queue:
		2614
		2615	=over 4
		2616
		2617	=item queueing from a signal handler context
		2618
		2619	To implement race-free queueing, you simply add to the queue in the signal
		2620	handler but you block the signal handler in the watcher callback. Here is
		2621	an example that does that for some fictitious SIGUSR1 handler:
		2622
		2623	static ev_async mysig;
		2624
		2625	static void
		2626	sigusr1_handler (void)
		2627	{
		2628	sometype data;
		2629
		2630	// no locking etc.
		2631	queue_put (data);
		2632	ev_async_send (EV_DEFAULT_ &mysig);
		2633	}
		2634
		2635	static void
		2636	mysig_cb (EV_P_ ev_async *w, int revents)
		2637	{
		2638	sometype data;
		2639	sigset_t block, prev;
		2640
		2641	sigemptyset (&block);
		2642	sigaddset (&block, SIGUSR1);
		2643	sigprocmask (SIG_BLOCK, &block, &prev);
		2644
		2645	while (queue_get (&data))
		2646	process (data);
		2647
		2648	if (sigismember (&prev, SIGUSR1)
		2649	sigprocmask (SIG_UNBLOCK, &block, 0);
		2650	}
		2651
		2652	(Note: pthreads in theory requires you to use C<pthread_setmask>
		2653	instead of C<sigprocmask> when you use threads, but libev doesn't do it
		2654	either...).
		2655
		2656	=item queueing from a thread context
		2657
		2658	The strategy for threads is different, as you cannot (easily) block
		2659	threads but you can easily preempt them, so to queue safely you need to
		2660	employ a traditional mutex lock, such as in this pthread example:
		2661
		2662	static ev_async mysig;
		2663	static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
		2664
		2665	static void
		2666	otherthread (void)
		2667	{
		2668	// only need to lock the actual queueing operation
		2669	pthread_mutex_lock (&mymutex);
		2670	queue_put (data);
		2671	pthread_mutex_unlock (&mymutex);
		2672
		2673	ev_async_send (EV_DEFAULT_ &mysig);
		2674	}
		2675
		2676	static void
		2677	mysig_cb (EV_P_ ev_async *w, int revents)
		2678	{
		2679	pthread_mutex_lock (&mymutex);
		2680
		2681	while (queue_get (&data))
		2682	process (data);
		2683
		2684	pthread_mutex_unlock (&mymutex);
		2685	}
		2686
		2687	=back
		2688
		2689
		2690	=head3 Watcher-Specific Functions and Data Members
		2691
		2692	=over 4
		2693
		2694	=item ev_async_init (ev_async *, callback)
		2695
		2696	Initialises and configures the async watcher - it has no parameters of any
		2697	kind. There is a C<ev_async_set> macro, but using it is utterly pointless,
		2698	trust me.
		2699
		2700	=item ev_async_send (loop, ev_async *)
		2701
		2702	Sends/signals/activates the given C<ev_async> watcher, that is, feeds
		2703	an C<EV_ASYNC> event on the watcher into the event loop. Unlike
		2704	C<ev_feed_event>, this call is safe to do from other threads, signal or
		2705	similar contexts (see the discussion of C<EV_ATOMIC_T> in the embedding
		2706	section below on what exactly this means).
		2707
		2708	Note that, as with other watchers in libev, multiple events might get
		2709	compressed into a single callback invocation (another way to look at this
		2710	is that C<ev_async> watchers are level-triggered, set on C<ev_async_send>,
		2711	reset when the event loop detects that).
		2712
		2713	This call incurs the overhead of a system call only once per event loop
		2714	iteration, so while the overhead might be noticeable, it doesn't apply to
		2715	repeated calls to C<ev_async_send> for the same event loop.
		2716
		2717	=item bool = ev_async_pending (ev_async *)
		2718
		2719	Returns a non-zero value when C<ev_async_send> has been called on the
		2720	watcher but the event has not yet been processed (or even noted) by the
		2721	event loop.
		2722
		2723	C<ev_async_send> sets a flag in the watcher and wakes up the loop. When
		2724	the loop iterates next and checks for the watcher to have become active,
		2725	it will reset the flag again. C<ev_async_pending> can be used to very
		2726	quickly check whether invoking the loop might be a good idea.
		2727
		2728	Not that this does I<not> check whether the watcher itself is pending,
		2729	only whether it has been requested to make this watcher pending: there
		2730	is a time window between the event loop checking and resetting the async
		2731	notification, and the callback being invoked.
		2732
		2733	=back
		2734
		2735
1870	=head1 OTHER FUNCTIONS	2736	=head1 OTHER FUNCTIONS
1871		2737
1872	There are some other functions of possible interest. Described. Here. Now.	2738	There are some other functions of possible interest. Described. Here. Now.
1873		2739
1874	=over 4	2740	=over 4
1875		2741
1876	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)	2742	=item ev_once (loop, int fd, int events, ev_tstamp timeout, callback)
1877		2743
1878	This function combines a simple timer and an I/O watcher, calls your	2744	This function combines a simple timer and an I/O watcher, calls your
1879	callback on whichever event happens first and automatically stop both	2745	callback on whichever event happens first and automatically stops both
1880	watchers. This is useful if you want to wait for a single event on an fd	2746	watchers. This is useful if you want to wait for a single event on an fd
1881	or timeout without having to allocate/configure/start/stop/free one or	2747	or timeout without having to allocate/configure/start/stop/free one or
1882	more watchers yourself.	2748	more watchers yourself.
1883		2749
1884	If C<fd> is less than 0, then no I/O watcher will be started and events	2750	If C<fd> is less than 0, then no I/O watcher will be started and the
1885	is being ignored. Otherwise, an C<ev_io> watcher for the given C<fd> and	2751	C<events> argument is being ignored. Otherwise, an C<ev_io> watcher for
1886	C<events> set will be craeted and started.	2752	the given C<fd> and C<events> set will be created and started.
1887		2753
1888	If C<timeout> is less than 0, then no timeout watcher will be	2754	If C<timeout> is less than 0, then no timeout watcher will be
1889	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and	2755	started. Otherwise an C<ev_timer> watcher with after = C<timeout> (and
1890	repeat = 0) will be started. While C<0> is a valid timeout, it is of	2756	repeat = 0) will be started. C<0> is a valid timeout.
1891	dubious value.
1892		2757
1893	The callback has the type C<void (*cb)(int revents, void *arg)> and gets	2758	The callback has the type C<void (*cb)(int revents, void *arg)> and gets
1894	passed an C<revents> set like normal event callbacks (a combination of	2759	passed an C<revents> set like normal event callbacks (a combination of
1895	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>	2760	C<EV_ERROR>, C<EV_READ>, C<EV_WRITE> or C<EV_TIMEOUT>) and the C<arg>
1896	value passed to C<ev_once>:	2761	value passed to C<ev_once>. Note that it is possible to receive I<both>
		2762	a timeout and an io event at the same time - you probably should give io
		2763	events precedence.
1897		2764
		2765	Example: wait up to ten seconds for data to appear on STDIN_FILENO.
		2766
1898	static void stdin_ready (int revents, void *arg)	2767	static void stdin_ready (int revents, void *arg)
1899	{	2768	{
1900	if (revents & EV_TIMEOUT)
1901	/* doh, nothing entered */;
1902	else if (revents & EV_READ)	2769	if (revents & EV_READ)
1903	/* stdin might have data for us, joy! */;	2770	/* stdin might have data for us, joy! */;
		2771	else if (revents & EV_TIMEOUT)
		2772	/* doh, nothing entered */;
1904	}	2773	}
1905		2774
1906	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);	2775	ev_once (STDIN_FILENO, EV_READ, 10., stdin_ready, 0);
1907		2776
1908	=item ev_feed_event (ev_loop *, watcher *, int revents)	2777	=item ev_feed_event (struct ev_loop *, watcher *, int revents)
1909		2778
1910	Feeds the given event set into the event loop, as if the specified event	2779	Feeds the given event set into the event loop, as if the specified event
1911	had happened for the specified watcher (which must be a pointer to an	2780	had happened for the specified watcher (which must be a pointer to an
1912	initialised but not necessarily started event watcher).	2781	initialised but not necessarily started event watcher).
1913		2782
1914	=item ev_feed_fd_event (ev_loop *, int fd, int revents)	2783	=item ev_feed_fd_event (struct ev_loop *, int fd, int revents)
1915		2784
1916	Feed an event on the given fd, as if a file descriptor backend detected	2785	Feed an event on the given fd, as if a file descriptor backend detected
1917	the given events it.	2786	the given events it.
1918		2787
1919	=item ev_feed_signal_event (ev_loop *loop, int signum)	2788	=item ev_feed_signal_event (struct ev_loop *loop, int signum)
1920		2789
1921	Feed an event as if the given signal occured (C<loop> must be the default	2790	Feed an event as if the given signal occurred (C<loop> must be the default
1922	loop!).	2791	loop!).
1923		2792
1924	=back	2793	=back
1925		2794
1926		2795
…		…
1942		2811
1943	=item * Priorities are not currently supported. Initialising priorities	2812	=item * Priorities are not currently supported. Initialising priorities
1944	will fail and all watchers will have the same priority, even though there	2813	will fail and all watchers will have the same priority, even though there
1945	is an ev_pri field.	2814	is an ev_pri field.
1946		2815
		2816	=item * In libevent, the last base created gets the signals, in libev, the
		2817	first base created (== the default loop) gets the signals.
		2818
1947	=item * Other members are not supported.	2819	=item * Other members are not supported.
1948		2820
1949	=item * The libev emulation is I<not> ABI compatible to libevent, you need	2821	=item * The libev emulation is I<not> ABI compatible to libevent, you need
1950	to use the libev header file and library.	2822	to use the libev header file and library.
1951		2823
1952	=back	2824	=back
1953		2825
1954	=head1 C++ SUPPORT	2826	=head1 C++ SUPPORT
1955		2827
1956	Libev comes with some simplistic wrapper classes for C++ that mainly allow	2828	Libev comes with some simplistic wrapper classes for C++ that mainly allow
1957	you to use some convinience methods to start/stop watchers and also change	2829	you to use some convenience methods to start/stop watchers and also change
1958	the callback model to a model using method callbacks on objects.	2830	the callback model to a model using method callbacks on objects.
1959		2831
1960	To use it,	2832	To use it,
1961		2833
1962	#include <ev++.h>	2834	#include <ev++.h>
1963		2835
1964	This automatically includes F<ev.h> and puts all of its definitions (many	2836	This automatically includes F<ev.h> and puts all of its definitions (many
1965	of them macros) into the global namespace. All C++ specific things are	2837	of them macros) into the global namespace. All C++ specific things are
1966	put into the C<ev> namespace. It should support all the same embedding	2838	put into the C<ev> namespace. It should support all the same embedding
1967	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.	2839	options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
…		…
2034	your compiler is good :), then the method will be fully inlined into the	2906	your compiler is good :), then the method will be fully inlined into the
2035	thunking function, making it as fast as a direct C callback.	2907	thunking function, making it as fast as a direct C callback.
2036		2908
2037	Example: simple class declaration and watcher initialisation	2909	Example: simple class declaration and watcher initialisation
2038		2910
2039	struct myclass	2911	struct myclass
2040	{	2912	{
2041	void io_cb (ev::io &w, int revents) { }	2913	void io_cb (ev::io &w, int revents) { }
2042	}	2914	}
2043		2915
2044	myclass obj;	2916	myclass obj;
2045	ev::io iow;	2917	ev::io iow;
2046	iow.set <myclass, &myclass::io_cb> (&obj);	2918	iow.set <myclass, &myclass::io_cb> (&obj);
		2919
		2920	=item w->set (object *)
		2921
		2922	This is an B<experimental> feature that might go away in a future version.
		2923
		2924	This is a variation of a method callback - leaving out the method to call
		2925	will default the method to C<operator ()>, which makes it possible to use
		2926	functor objects without having to manually specify the C<operator ()> all
		2927	the time. Incidentally, you can then also leave out the template argument
		2928	list.
		2929
		2930	The C<operator ()> method prototype must be C<void operator ()(watcher &w,
		2931	int revents)>.
		2932
		2933	See the method-C<set> above for more details.
		2934
		2935	Example: use a functor object as callback.
		2936
		2937	struct myfunctor
		2938	{
		2939	void operator() (ev::io &w, int revents)
		2940	{
		2941	...
		2942	}
		2943	}
		2944
		2945	myfunctor f;
		2946
		2947	ev::io w;
		2948	w.set (&f);
2047		2949
2048	=item w->set<function> (void *data = 0)	2950	=item w->set<function> (void *data = 0)
2049		2951
2050	Also sets a callback, but uses a static method or plain function as	2952	Also sets a callback, but uses a static method or plain function as
2051	callback. The optional C<data> argument will be stored in the watcher's	2953	callback. The optional C<data> argument will be stored in the watcher's
…		…
2053		2955
2054	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.	2956	The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
2055		2957
2056	See the method-C<set> above for more details.	2958	See the method-C<set> above for more details.
2057		2959
2058	Example:	2960	Example: Use a plain function as callback.
2059		2961
2060	static void io_cb (ev::io &w, int revents) { }	2962	static void io_cb (ev::io &w, int revents) { }
2061	iow.set <io_cb> ();	2963	iow.set <io_cb> ();
2062		2964
2063	=item w->set (struct ev_loop *)	2965	=item w->set (struct ev_loop *)
2064		2966
2065	Associates a different C<struct ev_loop> with this watcher. You can only	2967	Associates a different C<struct ev_loop> with this watcher. You can only
2066	do this when the watcher is inactive (and not pending either).	2968	do this when the watcher is inactive (and not pending either).
2067		2969
2068	=item w->set ([args])	2970	=item w->set ([arguments])
2069		2971
2070	Basically the same as C<ev_TYPE_set>, with the same args. Must be	2972	Basically the same as C<ev_TYPE_set>, with the same arguments. Must be
2071	called at least once. Unlike the C counterpart, an active watcher gets	2973	called at least once. Unlike the C counterpart, an active watcher gets
2072	automatically stopped and restarted when reconfiguring it with this	2974	automatically stopped and restarted when reconfiguring it with this
2073	method.	2975	method.
2074		2976
2075	=item w->start ()	2977	=item w->start ()
…		…
2099	=back	3001	=back
2100		3002
2101	Example: Define a class with an IO and idle watcher, start one of them in	3003	Example: Define a class with an IO and idle watcher, start one of them in
2102	the constructor.	3004	the constructor.
2103		3005
2104	class myclass	3006	class myclass
2105	{	3007	{
2106	ev_io io; void io_cb (ev::io &w, int revents);	3008	ev::io io ; void io_cb (ev::io &w, int revents);
2107	ev_idle idle void idle_cb (ev::idle &w, int revents);	3009	ev::idle idle; void idle_cb (ev::idle &w, int revents);
2108		3010
2109	myclass ();	3011	myclass (int fd)
2110	}	3012	{
2111
2112	myclass::myclass (int fd)
2113	{
2114	io .set <myclass, &myclass::io_cb > (this);	3013	io .set <myclass, &myclass::io_cb > (this);
2115	idle.set <myclass, &myclass::idle_cb> (this);	3014	idle.set <myclass, &myclass::idle_cb> (this);
2116		3015
2117	io.start (fd, ev::READ);	3016	io.start (fd, ev::READ);
		3017	}
2118	}	3018	};
		3019
		3020
		3021	=head1 OTHER LANGUAGE BINDINGS
		3022
		3023	Libev does not offer other language bindings itself, but bindings for a
		3024	number of languages exist in the form of third-party packages. If you know
		3025	any interesting language binding in addition to the ones listed here, drop
		3026	me a note.
		3027
		3028	=over 4
		3029
		3030	=item Perl
		3031
		3032	The EV module implements the full libev API and is actually used to test
		3033	libev. EV is developed together with libev. Apart from the EV core module,
		3034	there are additional modules that implement libev-compatible interfaces
		3035	to C<libadns> (C<EV::ADNS>, but C<AnyEvent::DNS> is preferred nowadays),
		3036	C<Net::SNMP> (C<Net::SNMP::EV>) and the C<libglib> event core (C<Glib::EV>
		3037	and C<EV::Glib>).
		3038
		3039	It can be found and installed via CPAN, its homepage is at
		3040	L<http://software.schmorp.de/pkg/EV>.
		3041
		3042	=item Python
		3043
		3044	Python bindings can be found at L<http://code.google.com/p/pyev/>. It
		3045	seems to be quite complete and well-documented.
		3046
		3047	=item Ruby
		3048
		3049	Tony Arcieri has written a ruby extension that offers access to a subset
		3050	of the libev API and adds file handle abstractions, asynchronous DNS and
		3051	more on top of it. It can be found via gem servers. Its homepage is at
		3052	L<http://rev.rubyforge.org/>.
		3053
		3054	Roger Pack reports that using the link order C<-lws2_32 -lmsvcrt-ruby-190>
		3055	makes rev work even on mingw.
		3056
		3057	=item Haskell
		3058
		3059	A haskell binding to libev is available at
		3060	L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>.
		3061
		3062	=item D
		3063
		3064	Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to
		3065	be found at L<http://proj.llucax.com.ar/wiki/evd>.
		3066
		3067	=item Ocaml
		3068
		3069	Erkki Seppala has written Ocaml bindings for libev, to be found at
		3070	L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>.
		3071
		3072	=back
2119		3073
2120		3074
2121	=head1 MACRO MAGIC	3075	=head1 MACRO MAGIC
2122		3076
2123	Libev can be compiled with a variety of options, the most fundamantal	3077	Libev can be compiled with a variety of options, the most fundamental
2124	of which is C<EV_MULTIPLICITY>. This option determines whether (most)	3078	of which is C<EV_MULTIPLICITY>. This option determines whether (most)
2125	functions and callbacks have an initial C<struct ev_loop *> argument.	3079	functions and callbacks have an initial C<struct ev_loop *> argument.
2126		3080
2127	To make it easier to write programs that cope with either variant, the	3081	To make it easier to write programs that cope with either variant, the
2128	following macros are defined:	3082	following macros are defined:
…		…
2133		3087
2134	This provides the loop I<argument> for functions, if one is required ("ev	3088	This provides the loop I<argument> for functions, if one is required ("ev
2135	loop argument"). The C<EV_A> form is used when this is the sole argument,	3089	loop argument"). The C<EV_A> form is used when this is the sole argument,
2136	C<EV_A_> is used when other arguments are following. Example:	3090	C<EV_A_> is used when other arguments are following. Example:
2137		3091
2138	ev_unref (EV_A);	3092	ev_unref (EV_A);
2139	ev_timer_add (EV_A_ watcher);	3093	ev_timer_add (EV_A_ watcher);
2140	ev_loop (EV_A_ 0);	3094	ev_loop (EV_A_ 0);
2141		3095
2142	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,	3096	It assumes the variable C<loop> of type C<struct ev_loop *> is in scope,
2143	which is often provided by the following macro.	3097	which is often provided by the following macro.
2144		3098
2145	=item C<EV_P>, C<EV_P_>	3099	=item C<EV_P>, C<EV_P_>
2146		3100
2147	This provides the loop I<parameter> for functions, if one is required ("ev	3101	This provides the loop I<parameter> for functions, if one is required ("ev
2148	loop parameter"). The C<EV_P> form is used when this is the sole parameter,	3102	loop parameter"). The C<EV_P> form is used when this is the sole parameter,
2149	C<EV_P_> is used when other parameters are following. Example:	3103	C<EV_P_> is used when other parameters are following. Example:
2150		3104
2151	// this is how ev_unref is being declared	3105	// this is how ev_unref is being declared
2152	static void ev_unref (EV_P);	3106	static void ev_unref (EV_P);
2153		3107
2154	// this is how you can declare your typical callback	3108	// this is how you can declare your typical callback
2155	static void cb (EV_P_ ev_timer *w, int revents)	3109	static void cb (EV_P_ ev_timer *w, int revents)
2156		3110
2157	It declares a parameter C<loop> of type C<struct ev_loop *>, quite	3111	It declares a parameter C<loop> of type C<struct ev_loop *>, quite
2158	suitable for use with C<EV_A>.	3112	suitable for use with C<EV_A>.
2159		3113
2160	=item C<EV_DEFAULT>, C<EV_DEFAULT_>	3114	=item C<EV_DEFAULT>, C<EV_DEFAULT_>
2161		3115
2162	Similar to the other two macros, this gives you the value of the default	3116	Similar to the other two macros, this gives you the value of the default
2163	loop, if multiple loops are supported ("ev loop default").	3117	loop, if multiple loops are supported ("ev loop default").
		3118
		3119	=item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_>
		3120
		3121	Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the
		3122	default loop has been initialised (C<UC> == unchecked). Their behaviour
		3123	is undefined when the default loop has not been initialised by a previous
		3124	execution of C<EV_DEFAULT>, C<EV_DEFAULT_> or C<ev_default_init (...)>.
		3125
		3126	It is often prudent to use C<EV_DEFAULT> when initialising the first
		3127	watcher in a function but use C<EV_DEFAULT_UC> afterwards.
2164		3128
2165	=back	3129	=back
2166		3130
2167	Example: Declare and initialise a check watcher, utilising the above	3131	Example: Declare and initialise a check watcher, utilising the above
2168	macros so it will work regardless of whether multiple loops are supported	3132	macros so it will work regardless of whether multiple loops are supported
2169	or not.	3133	or not.
2170		3134
2171	static void	3135	static void
2172	check_cb (EV_P_ ev_timer *w, int revents)	3136	check_cb (EV_P_ ev_timer *w, int revents)
2173	{	3137	{
2174	ev_check_stop (EV_A_ w);	3138	ev_check_stop (EV_A_ w);
2175	}	3139	}
2176		3140
2177	ev_check check;	3141	ev_check check;
2178	ev_check_init (&check, check_cb);	3142	ev_check_init (&check, check_cb);
2179	ev_check_start (EV_DEFAULT_ &check);	3143	ev_check_start (EV_DEFAULT_ &check);
2180	ev_loop (EV_DEFAULT_ 0);	3144	ev_loop (EV_DEFAULT_ 0);
2181		3145
2182	=head1 EMBEDDING	3146	=head1 EMBEDDING
2183		3147
2184	Libev can (and often is) directly embedded into host	3148	Libev can (and often is) directly embedded into host
2185	applications. Examples of applications that embed it include the Deliantra	3149	applications. Examples of applications that embed it include the Deliantra
…		…
2192	libev somewhere in your source tree).	3156	libev somewhere in your source tree).
2193		3157
2194	=head2 FILESETS	3158	=head2 FILESETS
2195		3159
2196	Depending on what features you need you need to include one or more sets of files	3160	Depending on what features you need you need to include one or more sets of files
2197	in your app.	3161	in your application.
2198		3162
2199	=head3 CORE EVENT LOOP	3163	=head3 CORE EVENT LOOP
2200		3164
2201	To include only the libev core (all the C<ev_*> functions), with manual	3165	To include only the libev core (all the C<ev_*> functions), with manual
2202	configuration (no autoconf):	3166	configuration (no autoconf):
2203		3167
2204	#define EV_STANDALONE 1	3168	#define EV_STANDALONE 1
2205	#include "ev.c"	3169	#include "ev.c"
2206		3170
2207	This will automatically include F<ev.h>, too, and should be done in a	3171	This will automatically include F<ev.h>, too, and should be done in a
2208	single C source file only to provide the function implementations. To use	3172	single C source file only to provide the function implementations. To use
2209	it, do the same for F<ev.h> in all files wishing to use this API (best	3173	it, do the same for F<ev.h> in all files wishing to use this API (best
2210	done by writing a wrapper around F<ev.h> that you can include instead and	3174	done by writing a wrapper around F<ev.h> that you can include instead and
2211	where you can put other configuration options):	3175	where you can put other configuration options):
2212		3176
2213	#define EV_STANDALONE 1	3177	#define EV_STANDALONE 1
2214	#include "ev.h"	3178	#include "ev.h"
2215		3179
2216	Both header files and implementation files can be compiled with a C++	3180	Both header files and implementation files can be compiled with a C++
2217	compiler (at least, thats a stated goal, and breakage will be treated	3181	compiler (at least, that's a stated goal, and breakage will be treated
2218	as a bug).	3182	as a bug).
2219		3183
2220	You need the following files in your source tree, or in a directory	3184	You need the following files in your source tree, or in a directory
2221	in your include path (e.g. in libev/ when using -Ilibev):	3185	in your include path (e.g. in libev/ when using -Ilibev):
2222		3186
2223	ev.h	3187	ev.h
2224	ev.c	3188	ev.c
2225	ev_vars.h	3189	ev_vars.h
2226	ev_wrap.h	3190	ev_wrap.h
2227		3191
2228	ev_win32.c required on win32 platforms only	3192	ev_win32.c required on win32 platforms only
2229		3193
2230	ev_select.c only when select backend is enabled (which is enabled by default)	3194	ev_select.c only when select backend is enabled (which is enabled by default)
2231	ev_poll.c only when poll backend is enabled (disabled by default)	3195	ev_poll.c only when poll backend is enabled (disabled by default)
2232	ev_epoll.c only when the epoll backend is enabled (disabled by default)	3196	ev_epoll.c only when the epoll backend is enabled (disabled by default)
2233	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)	3197	ev_kqueue.c only when the kqueue backend is enabled (disabled by default)
2234	ev_port.c only when the solaris port backend is enabled (disabled by default)	3198	ev_port.c only when the solaris port backend is enabled (disabled by default)
2235		3199
2236	F<ev.c> includes the backend files directly when enabled, so you only need	3200	F<ev.c> includes the backend files directly when enabled, so you only need
2237	to compile this single file.	3201	to compile this single file.
2238		3202
2239	=head3 LIBEVENT COMPATIBILITY API	3203	=head3 LIBEVENT COMPATIBILITY API
2240		3204
2241	To include the libevent compatibility API, also include:	3205	To include the libevent compatibility API, also include:
2242		3206
2243	#include "event.c"	3207	#include "event.c"
2244		3208
2245	in the file including F<ev.c>, and:	3209	in the file including F<ev.c>, and:
2246		3210
2247	#include "event.h"	3211	#include "event.h"
2248		3212
2249	in the files that want to use the libevent API. This also includes F<ev.h>.	3213	in the files that want to use the libevent API. This also includes F<ev.h>.
2250		3214
2251	You need the following additional files for this:	3215	You need the following additional files for this:
2252		3216
2253	event.h	3217	event.h
2254	event.c	3218	event.c
2255		3219
2256	=head3 AUTOCONF SUPPORT	3220	=head3 AUTOCONF SUPPORT
2257		3221
2258	Instead of using C<EV_STANDALONE=1> and providing your config in	3222	Instead of using C<EV_STANDALONE=1> and providing your configuration in
2259	whatever way you want, you can also C<m4_include([libev.m4])> in your	3223	whatever way you want, you can also C<m4_include([libev.m4])> in your
2260	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then	3224	F<configure.ac> and leave C<EV_STANDALONE> undefined. F<ev.c> will then
2261	include F<config.h> and configure itself accordingly.	3225	include F<config.h> and configure itself accordingly.
2262		3226
2263	For this of course you need the m4 file:	3227	For this of course you need the m4 file:
2264		3228
2265	libev.m4	3229	libev.m4
2266		3230
2267	=head2 PREPROCESSOR SYMBOLS/MACROS	3231	=head2 PREPROCESSOR SYMBOLS/MACROS
2268		3232
2269	Libev can be configured via a variety of preprocessor symbols you have to define	3233	Libev can be configured via a variety of preprocessor symbols you have to
2270	before including any of its files. The default is not to build for multiplicity	3234	define before including any of its files. The default in the absence of
2271	and only include the select backend.	3235	autoconf is documented for every option.
2272		3236
2273	=over 4	3237	=over 4
2274		3238
2275	=item EV_STANDALONE	3239	=item EV_STANDALONE
2276		3240
…		…
2278	keeps libev from including F<config.h>, and it also defines dummy	3242	keeps libev from including F<config.h>, and it also defines dummy
2279	implementations for some libevent functions (such as logging, which is not	3243	implementations for some libevent functions (such as logging, which is not
2280	supported). It will also not define any of the structs usually found in	3244	supported). It will also not define any of the structs usually found in
2281	F<event.h> that are not directly supported by the libev core alone.	3245	F<event.h> that are not directly supported by the libev core alone.
2282		3246
		3247	In stanbdalone mode, libev will still try to automatically deduce the
		3248	configuration, but has to be more conservative.
		3249
2283	=item EV_USE_MONOTONIC	3250	=item EV_USE_MONOTONIC
2284		3251
2285	If defined to be C<1>, libev will try to detect the availability of the	3252	If defined to be C<1>, libev will try to detect the availability of the
2286	monotonic clock option at both compiletime and runtime. Otherwise no use	3253	monotonic clock option at both compile time and runtime. Otherwise no
2287	of the monotonic clock option will be attempted. If you enable this, you	3254	use of the monotonic clock option will be attempted. If you enable this,
2288	usually have to link against librt or something similar. Enabling it when	3255	you usually have to link against librt or something similar. Enabling it
2289	the functionality isn't available is safe, though, although you have	3256	when the functionality isn't available is safe, though, although you have
2290	to make sure you link against any libraries where the C<clock_gettime>	3257	to make sure you link against any libraries where the C<clock_gettime>
2291	function is hiding in (often F<-lrt>).	3258	function is hiding in (often F<-lrt>). See also C<EV_USE_CLOCK_SYSCALL>.
2292		3259
2293	=item EV_USE_REALTIME	3260	=item EV_USE_REALTIME
2294		3261
2295	If defined to be C<1>, libev will try to detect the availability of the	3262	If defined to be C<1>, libev will try to detect the availability of the
2296	realtime clock option at compiletime (and assume its availability at	3263	real-time clock option at compile time (and assume its availability
2297	runtime if successful). Otherwise no use of the realtime clock option will	3264	at runtime if successful). Otherwise no use of the real-time clock
2298	be attempted. This effectively replaces C<gettimeofday> by C<clock_get	3265	option will be attempted. This effectively replaces C<gettimeofday>
2299	(CLOCK_REALTIME, ...)> and will not normally affect correctness. See the	3266	by C<clock_get (CLOCK_REALTIME, ...)> and will not normally affect
2300	note about libraries in the description of C<EV_USE_MONOTONIC>, though.	3267	correctness. See the note about libraries in the description of
		3268	C<EV_USE_MONOTONIC>, though. Defaults to the opposite value of
		3269	C<EV_USE_CLOCK_SYSCALL>.
		3270
		3271	=item EV_USE_CLOCK_SYSCALL
		3272
		3273	If defined to be C<1>, libev will try to use a direct syscall instead
		3274	of calling the system-provided C<clock_gettime> function. This option
		3275	exists because on GNU/Linux, C<clock_gettime> is in C<librt>, but C<librt>
		3276	unconditionally pulls in C<libpthread>, slowing down single-threaded
		3277	programs needlessly. Using a direct syscall is slightly slower (in
		3278	theory), because no optimised vdso implementation can be used, but avoids
		3279	the pthread dependency. Defaults to C<1> on GNU/Linux with glibc 2.x or
		3280	higher, as it simplifies linking (no need for C<-lrt>).
		3281
		3282	=item EV_USE_NANOSLEEP
		3283
		3284	If defined to be C<1>, libev will assume that C<nanosleep ()> is available
		3285	and will use it for delays. Otherwise it will use C<select ()>.
		3286
		3287	=item EV_USE_EVENTFD
		3288
		3289	If defined to be C<1>, then libev will assume that C<eventfd ()> is
		3290	available and will probe for kernel support at runtime. This will improve
		3291	C<ev_signal> and C<ev_async> performance and reduce resource consumption.
		3292	If undefined, it will be enabled if the headers indicate GNU/Linux + Glibc
		3293	2.7 or newer, otherwise disabled.
2301		3294
2302	=item EV_USE_SELECT	3295	=item EV_USE_SELECT
2303		3296
2304	If undefined or defined to be C<1>, libev will compile in support for the	3297	If undefined or defined to be C<1>, libev will compile in support for the
2305	C<select>(2) backend. No attempt at autodetection will be done: if no	3298	C<select>(2) backend. No attempt at auto-detection will be done: if no
2306	other method takes over, select will be it. Otherwise the select backend	3299	other method takes over, select will be it. Otherwise the select backend
2307	will not be compiled in.	3300	will not be compiled in.
2308		3301
2309	=item EV_SELECT_USE_FD_SET	3302	=item EV_SELECT_USE_FD_SET
2310		3303
2311	If defined to C<1>, then the select backend will use the system C<fd_set>	3304	If defined to C<1>, then the select backend will use the system C<fd_set>
2312	structure. This is useful if libev doesn't compile due to a missing	3305	structure. This is useful if libev doesn't compile due to a missing
2313	C<NFDBITS> or C<fd_mask> definition or it misguesses the bitset layout on	3306	C<NFDBITS> or C<fd_mask> definition or it mis-guesses the bitset layout
2314	exotic systems. This usually limits the range of file descriptors to some	3307	on exotic systems. This usually limits the range of file descriptors to
2315	low limit such as 1024 or might have other limitations (winsocket only	3308	some low limit such as 1024 or might have other limitations (winsocket
2316	allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation, might	3309	only allows 64 sockets). The C<FD_SETSIZE> macro, set before compilation,
2317	influence the size of the C<fd_set> used.	3310	configures the maximum size of the C<fd_set>.
2318		3311
2319	=item EV_SELECT_IS_WINSOCKET	3312	=item EV_SELECT_IS_WINSOCKET
2320		3313
2321	When defined to C<1>, the select backend will assume that	3314	When defined to C<1>, the select backend will assume that
2322	select/socket/connect etc. don't understand file descriptors but	3315	select/socket/connect etc. don't understand file descriptors but
…		…
2324	be used is the winsock select). This means that it will call	3317	be used is the winsock select). This means that it will call
2325	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,	3318	C<_get_osfhandle> on the fd to convert it to an OS handle. Otherwise,
2326	it is assumed that all these functions actually work on fds, even	3319	it is assumed that all these functions actually work on fds, even
2327	on win32. Should not be defined on non-win32 platforms.	3320	on win32. Should not be defined on non-win32 platforms.
2328		3321
		3322	=item EV_FD_TO_WIN32_HANDLE
		3323
		3324	If C<EV_SELECT_IS_WINSOCKET> is enabled, then libev needs a way to map
		3325	file descriptors to socket handles. When not defining this symbol (the
		3326	default), then libev will call C<_get_osfhandle>, which is usually
		3327	correct. In some cases, programs use their own file descriptor management,
		3328	in which case they can provide this function to map fds to socket handles.
		3329
2329	=item EV_USE_POLL	3330	=item EV_USE_POLL
2330		3331
2331	If defined to be C<1>, libev will compile in support for the C<poll>(2)	3332	If defined to be C<1>, libev will compile in support for the C<poll>(2)
2332	backend. Otherwise it will be enabled on non-win32 platforms. It	3333	backend. Otherwise it will be enabled on non-win32 platforms. It
2333	takes precedence over select.	3334	takes precedence over select.
2334		3335
2335	=item EV_USE_EPOLL	3336	=item EV_USE_EPOLL
2336		3337
2337	If defined to be C<1>, libev will compile in support for the Linux	3338	If defined to be C<1>, libev will compile in support for the Linux
2338	C<epoll>(7) backend. Its availability will be detected at runtime,	3339	C<epoll>(7) backend. Its availability will be detected at runtime,
2339	otherwise another method will be used as fallback. This is the	3340	otherwise another method will be used as fallback. This is the preferred
2340	preferred backend for GNU/Linux systems.	3341	backend for GNU/Linux systems. If undefined, it will be enabled if the
		3342	headers indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
2341		3343
2342	=item EV_USE_KQUEUE	3344	=item EV_USE_KQUEUE
2343		3345
2344	If defined to be C<1>, libev will compile in support for the BSD style	3346	If defined to be C<1>, libev will compile in support for the BSD style
2345	C<kqueue>(2) backend. Its actual availability will be detected at runtime,	3347	C<kqueue>(2) backend. Its actual availability will be detected at runtime,
…		…
2358	otherwise another method will be used as fallback. This is the preferred	3360	otherwise another method will be used as fallback. This is the preferred
2359	backend for Solaris 10 systems.	3361	backend for Solaris 10 systems.
2360		3362
2361	=item EV_USE_DEVPOLL	3363	=item EV_USE_DEVPOLL
2362		3364
2363	reserved for future expansion, works like the USE symbols above.	3365	Reserved for future expansion, works like the USE symbols above.
2364		3366
2365	=item EV_USE_INOTIFY	3367	=item EV_USE_INOTIFY
2366		3368
2367	If defined to be C<1>, libev will compile in support for the Linux inotify	3369	If defined to be C<1>, libev will compile in support for the Linux inotify
2368	interface to speed up C<ev_stat> watchers. Its actual availability will	3370	interface to speed up C<ev_stat> watchers. Its actual availability will
2369	be detected at runtime.	3371	be detected at runtime. If undefined, it will be enabled if the headers
		3372	indicate GNU/Linux + Glibc 2.4 or newer, otherwise disabled.
		3373
		3374	=item EV_ATOMIC_T
		3375
		3376	Libev requires an integer type (suitable for storing C<0> or C<1>) whose
		3377	access is atomic with respect to other threads or signal contexts. No such
		3378	type is easily found in the C language, so you can provide your own type
		3379	that you know is safe for your purposes. It is used both for signal handler "locking"
		3380	as well as for signal and thread safety in C<ev_async> watchers.
		3381
		3382	In the absence of this define, libev will use C<sig_atomic_t volatile>
		3383	(from F<signal.h>), which is usually good enough on most platforms.
2370		3384
2371	=item EV_H	3385	=item EV_H
2372		3386
2373	The name of the F<ev.h> header file used to include it. The default if	3387	The name of the F<ev.h> header file used to include it. The default if
2374	undefined is C<< <ev.h> >> in F<event.h> and C<"ev.h"> in F<ev.c>. This	3388	undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be
2375	can be used to virtually rename the F<ev.h> header file in case of conflicts.	3389	used to virtually rename the F<ev.h> header file in case of conflicts.
2376		3390
2377	=item EV_CONFIG_H	3391	=item EV_CONFIG_H
2378		3392
2379	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override	3393	If C<EV_STANDALONE> isn't C<1>, this variable can be used to override
2380	F<ev.c>'s idea of where to find the F<config.h> file, similarly to	3394	F<ev.c>'s idea of where to find the F<config.h> file, similarly to
2381	C<EV_H>, above.	3395	C<EV_H>, above.
2382		3396
2383	=item EV_EVENT_H	3397	=item EV_EVENT_H
2384		3398
2385	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea	3399	Similarly to C<EV_H>, this macro can be used to override F<event.c>'s idea
2386	of how the F<event.h> header can be found.	3400	of how the F<event.h> header can be found, the default is C<"event.h">.
2387		3401
2388	=item EV_PROTOTYPES	3402	=item EV_PROTOTYPES
2389		3403
2390	If defined to be C<0>, then F<ev.h> will not define any function	3404	If defined to be C<0>, then F<ev.h> will not define any function
2391	prototypes, but still define all the structs and other symbols. This is	3405	prototypes, but still define all the structs and other symbols. This is
…		…
2412	When doing priority-based operations, libev usually has to linearly search	3426	When doing priority-based operations, libev usually has to linearly search
2413	all the priorities, so having many of them (hundreds) uses a lot of space	3427	all the priorities, so having many of them (hundreds) uses a lot of space
2414	and time, so using the defaults of five priorities (-2 .. +2) is usually	3428	and time, so using the defaults of five priorities (-2 .. +2) is usually
2415	fine.	3429	fine.
2416		3430
2417	If your embedding app does not need any priorities, defining these both to	3431	If your embedding application does not need any priorities, defining these
2418	C<0> will save some memory and cpu.	3432	both to C<0> will save some memory and CPU.
2419		3433
2420	=item EV_PERIODIC_ENABLE	3434	=item EV_PERIODIC_ENABLE
2421		3435
2422	If undefined or defined to be C<1>, then periodic timers are supported. If	3436	If undefined or defined to be C<1>, then periodic timers are supported. If
2423	defined to be C<0>, then they are not. Disabling them saves a few kB of	3437	defined to be C<0>, then they are not. Disabling them saves a few kB of
…		…
2430	code.	3444	code.
2431		3445
2432	=item EV_EMBED_ENABLE	3446	=item EV_EMBED_ENABLE
2433		3447
2434	If undefined or defined to be C<1>, then embed watchers are supported. If	3448	If undefined or defined to be C<1>, then embed watchers are supported. If
2435	defined to be C<0>, then they are not.	3449	defined to be C<0>, then they are not. Embed watchers rely on most other
		3450	watcher types, which therefore must not be disabled.
2436		3451
2437	=item EV_STAT_ENABLE	3452	=item EV_STAT_ENABLE
2438		3453
2439	If undefined or defined to be C<1>, then stat watchers are supported. If	3454	If undefined or defined to be C<1>, then stat watchers are supported. If
2440	defined to be C<0>, then they are not.	3455	defined to be C<0>, then they are not.
…		…
2442	=item EV_FORK_ENABLE	3457	=item EV_FORK_ENABLE
2443		3458
2444	If undefined or defined to be C<1>, then fork watchers are supported. If	3459	If undefined or defined to be C<1>, then fork watchers are supported. If
2445	defined to be C<0>, then they are not.	3460	defined to be C<0>, then they are not.
2446		3461
		3462	=item EV_ASYNC_ENABLE
		3463
		3464	If undefined or defined to be C<1>, then async watchers are supported. If
		3465	defined to be C<0>, then they are not.
		3466
2447	=item EV_MINIMAL	3467	=item EV_MINIMAL
2448		3468
2449	If you need to shave off some kilobytes of code at the expense of some	3469	If you need to shave off some kilobytes of code at the expense of some
2450	speed, define this symbol to C<1>. Currently only used for gcc to override	3470	speed, define this symbol to C<1>. Currently this is used to override some
2451	some inlining decisions, saves roughly 30% codesize of amd64.	3471	inlining decisions, saves roughly 30% code size on amd64. It also selects a
		3472	much smaller 2-heap for timer management over the default 4-heap.
2452		3473
2453	=item EV_PID_HASHSIZE	3474	=item EV_PID_HASHSIZE
2454		3475
2455	C<ev_child> watchers use a small hash table to distribute workload by	3476	C<ev_child> watchers use a small hash table to distribute workload by
2456	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more	3477	pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
2457	than enough. If you need to manage thousands of children you might want to	3478	than enough. If you need to manage thousands of children you might want to
2458	increase this value (I<must> be a power of two).	3479	increase this value (I<must> be a power of two).
2459		3480
2460	=item EV_INOTIFY_HASHSIZE	3481	=item EV_INOTIFY_HASHSIZE
2461		3482
2462	C<ev_staz> watchers use a small hash table to distribute workload by	3483	C<ev_stat> watchers use a small hash table to distribute workload by
2463	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),	3484	inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
2464	usually more than enough. If you need to manage thousands of C<ev_stat>	3485	usually more than enough. If you need to manage thousands of C<ev_stat>
2465	watchers you might want to increase this value (I<must> be a power of	3486	watchers you might want to increase this value (I<must> be a power of
2466	two).	3487	two).
2467		3488
		3489	=item EV_USE_4HEAP
		3490
		3491	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3492	timer and periodics heaps, libev uses a 4-heap when this symbol is defined
		3493	to C<1>. The 4-heap uses more complicated (longer) code but has noticeably
		3494	faster performance with many (thousands) of watchers.
		3495
		3496	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3497	(disabled).
		3498
		3499	=item EV_HEAP_CACHE_AT
		3500
		3501	Heaps are not very cache-efficient. To improve the cache-efficiency of the
		3502	timer and periodics heaps, libev can cache the timestamp (I<at>) within
		3503	the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>),
		3504	which uses 8-12 bytes more per watcher and a few hundred bytes more code,
		3505	but avoids random read accesses on heap changes. This improves performance
		3506	noticeably with many (hundreds) of watchers.
		3507
		3508	The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0>
		3509	(disabled).
		3510
		3511	=item EV_VERIFY
		3512
		3513	Controls how much internal verification (see C<ev_loop_verify ()>) will
		3514	be done: If set to C<0>, no internal verification code will be compiled
		3515	in. If set to C<1>, then verification code will be compiled in, but not
		3516	called. If set to C<2>, then the internal verification code will be
		3517	called once per loop, which can slow down libev. If set to C<3>, then the
		3518	verification code will be called very frequently, which will slow down
		3519	libev considerably.
		3520
		3521	The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be
		3522	C<0>.
		3523
2468	=item EV_COMMON	3524	=item EV_COMMON
2469		3525
2470	By default, all watchers have a C<void *data> member. By redefining	3526	By default, all watchers have a C<void *data> member. By redefining
2471	this macro to a something else you can include more and other types of	3527	this macro to a something else you can include more and other types of
2472	members. You have to define it each time you include one of the files,	3528	members. You have to define it each time you include one of the files,
2473	though, and it must be identical each time.	3529	though, and it must be identical each time.
2474		3530
2475	For example, the perl EV module uses something like this:	3531	For example, the perl EV module uses something like this:
2476		3532
2477	#define EV_COMMON \	3533	#define EV_COMMON \
2478	SV *self; /* contains this struct */ \	3534	SV *self; /* contains this struct */ \
2479	SV *cb_sv, *fh /* note no trailing ";" */	3535	SV *cb_sv, *fh /* note no trailing ";" */
2480		3536
2481	=item EV_CB_DECLARE (type)	3537	=item EV_CB_DECLARE (type)
2482		3538
2483	=item EV_CB_INVOKE (watcher, revents)	3539	=item EV_CB_INVOKE (watcher, revents)
2484		3540
…		…
2489	definition and a statement, respectively. See the F<ev.h> header file for	3545	definition and a statement, respectively. See the F<ev.h> header file for
2490	their default definitions. One possible use for overriding these is to	3546	their default definitions. One possible use for overriding these is to
2491	avoid the C<struct ev_loop *> as first argument in all cases, or to use	3547	avoid the C<struct ev_loop *> as first argument in all cases, or to use
2492	method calls instead of plain function calls in C++.	3548	method calls instead of plain function calls in C++.
2493		3549
		3550	=back
		3551
2494	=head2 EXPORTED API SYMBOLS	3552	=head2 EXPORTED API SYMBOLS
2495		3553
2496	If you need to re-export the API (e.g. via a dll) and you need a list of	3554	If you need to re-export the API (e.g. via a DLL) and you need a list of
2497	exported symbols, you can use the provided F<Symbol.*> files which list	3555	exported symbols, you can use the provided F<Symbol.*> files which list
2498	all public symbols, one per line:	3556	all public symbols, one per line:
2499		3557
2500	Symbols.ev for libev proper	3558	Symbols.ev for libev proper
2501	Symbols.event for the libevent emulation	3559	Symbols.event for the libevent emulation
2502		3560
2503	This can also be used to rename all public symbols to avoid clashes with	3561	This can also be used to rename all public symbols to avoid clashes with
2504	multiple versions of libev linked together (which is obviously bad in	3562	multiple versions of libev linked together (which is obviously bad in
2505	itself, but sometimes it is inconvinient to avoid this).	3563	itself, but sometimes it is inconvenient to avoid this).
2506		3564
2507	A sed command like this will create wrapper C<#define>'s that you need to	3565	A sed command like this will create wrapper C<#define>'s that you need to
2508	include before including F<ev.h>:	3566	include before including F<ev.h>:
2509		3567
2510	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h	3568	<Symbols.ev sed -e "s/.*/#define & myprefix_&/" >wrap.h
…		…
2527	file.	3585	file.
2528		3586
2529	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file	3587	The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
2530	that everybody includes and which overrides some configure choices:	3588	that everybody includes and which overrides some configure choices:
2531		3589
2532	#define EV_MINIMAL 1	3590	#define EV_MINIMAL 1
2533	#define EV_USE_POLL 0	3591	#define EV_USE_POLL 0
2534	#define EV_MULTIPLICITY 0	3592	#define EV_MULTIPLICITY 0
2535	#define EV_PERIODIC_ENABLE 0	3593	#define EV_PERIODIC_ENABLE 0
2536	#define EV_STAT_ENABLE 0	3594	#define EV_STAT_ENABLE 0
2537	#define EV_FORK_ENABLE 0	3595	#define EV_FORK_ENABLE 0
2538	#define EV_CONFIG_H <config.h>	3596	#define EV_CONFIG_H <config.h>
2539	#define EV_MINPRI 0	3597	#define EV_MINPRI 0
2540	#define EV_MAXPRI 0	3598	#define EV_MAXPRI 0
2541		3599
2542	#include "ev++.h"	3600	#include "ev++.h"
2543		3601
2544	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:	3602	And a F<ev_cpp.C> implementation file that contains libev proper and is compiled:
2545		3603
2546	#include "ev_cpp.h"	3604	#include "ev_cpp.h"
2547	#include "ev.c"	3605	#include "ev.c"
2548		3606
		3607	=head1 INTERACTION WITH OTHER PROGRAMS OR LIBRARIES
2549		3608
		3609	=head2 THREADS AND COROUTINES
		3610
		3611	=head3 THREADS
		3612
		3613	All libev functions are reentrant and thread-safe unless explicitly
		3614	documented otherwise, but libev implements no locking itself. This means
		3615	that you can use as many loops as you want in parallel, as long as there
		3616	are no concurrent calls into any libev function with the same loop
		3617	parameter (C<ev_default_*> calls have an implicit default loop parameter,
		3618	of course): libev guarantees that different event loops share no data
		3619	structures that need any locking.
		3620
		3621	Or to put it differently: calls with different loop parameters can be done
		3622	concurrently from multiple threads, calls with the same loop parameter
		3623	must be done serially (but can be done from different threads, as long as
		3624	only one thread ever is inside a call at any point in time, e.g. by using
		3625	a mutex per loop).
		3626
		3627	Specifically to support threads (and signal handlers), libev implements
		3628	so-called C<ev_async> watchers, which allow some limited form of
		3629	concurrency on the same event loop, namely waking it up "from the
		3630	outside".
		3631
		3632	If you want to know which design (one loop, locking, or multiple loops
		3633	without or something else still) is best for your problem, then I cannot
		3634	help you, but here is some generic advice:
		3635
		3636	=over 4
		3637
		3638	=item * most applications have a main thread: use the default libev loop
		3639	in that thread, or create a separate thread running only the default loop.
		3640
		3641	This helps integrating other libraries or software modules that use libev
		3642	themselves and don't care/know about threading.
		3643
		3644	=item * one loop per thread is usually a good model.
		3645
		3646	Doing this is almost never wrong, sometimes a better-performance model
		3647	exists, but it is always a good start.
		3648
		3649	=item * other models exist, such as the leader/follower pattern, where one
		3650	loop is handed through multiple threads in a kind of round-robin fashion.
		3651
		3652	Choosing a model is hard - look around, learn, know that usually you can do
		3653	better than you currently do :-)
		3654
		3655	=item * often you need to talk to some other thread which blocks in the
		3656	event loop.
		3657
		3658	C<ev_async> watchers can be used to wake them up from other threads safely
		3659	(or from signal contexts...).
		3660
		3661	An example use would be to communicate signals or other events that only
		3662	work in the default loop by registering the signal watcher with the
		3663	default loop and triggering an C<ev_async> watcher from the default loop
		3664	watcher callback into the event loop interested in the signal.
		3665
		3666	=back
		3667
		3668	=head3 COROUTINES
		3669
		3670	Libev is very accommodating to coroutines ("cooperative threads"):
		3671	libev fully supports nesting calls to its functions from different
		3672	coroutines (e.g. you can call C<ev_loop> on the same loop from two
		3673	different coroutines, and switch freely between both coroutines running the
		3674	loop, as long as you don't confuse yourself). The only exception is that
		3675	you must not do this from C<ev_periodic> reschedule callbacks.
		3676
		3677	Care has been taken to ensure that libev does not keep local state inside
		3678	C<ev_loop>, and other calls do not usually allow for coroutine switches as
		3679	they do not call any callbacks.
		3680
		3681	=head2 COMPILER WARNINGS
		3682
		3683	Depending on your compiler and compiler settings, you might get no or a
		3684	lot of warnings when compiling libev code. Some people are apparently
		3685	scared by this.
		3686
		3687	However, these are unavoidable for many reasons. For one, each compiler
		3688	has different warnings, and each user has different tastes regarding
		3689	warning options. "Warn-free" code therefore cannot be a goal except when
		3690	targeting a specific compiler and compiler-version.
		3691
		3692	Another reason is that some compiler warnings require elaborate
		3693	workarounds, or other changes to the code that make it less clear and less
		3694	maintainable.
		3695
		3696	And of course, some compiler warnings are just plain stupid, or simply
		3697	wrong (because they don't actually warn about the condition their message
		3698	seems to warn about). For example, certain older gcc versions had some
		3699	warnings that resulted an extreme number of false positives. These have
		3700	been fixed, but some people still insist on making code warn-free with
		3701	such buggy versions.
		3702
		3703	While libev is written to generate as few warnings as possible,
		3704	"warn-free" code is not a goal, and it is recommended not to build libev
		3705	with any compiler warnings enabled unless you are prepared to cope with
		3706	them (e.g. by ignoring them). Remember that warnings are just that:
		3707	warnings, not errors, or proof of bugs.
		3708
		3709
		3710	=head2 VALGRIND
		3711
		3712	Valgrind has a special section here because it is a popular tool that is
		3713	highly useful. Unfortunately, valgrind reports are very hard to interpret.
		3714
		3715	If you think you found a bug (memory leak, uninitialised data access etc.)
		3716	in libev, then check twice: If valgrind reports something like:
		3717
		3718	==2274== definitely lost: 0 bytes in 0 blocks.
		3719	==2274== possibly lost: 0 bytes in 0 blocks.
		3720	==2274== still reachable: 256 bytes in 1 blocks.
		3721
		3722	Then there is no memory leak, just as memory accounted to global variables
		3723	is not a memleak - the memory is still being referenced, and didn't leak.
		3724
		3725	Similarly, under some circumstances, valgrind might report kernel bugs
		3726	as if it were a bug in libev (e.g. in realloc or in the poll backend,
		3727	although an acceptable workaround has been found here), or it might be
		3728	confused.
		3729
		3730	Keep in mind that valgrind is a very good tool, but only a tool. Don't
		3731	make it into some kind of religion.
		3732
		3733	If you are unsure about something, feel free to contact the mailing list
		3734	with the full valgrind report and an explanation on why you think this
		3735	is a bug in libev (best check the archives, too :). However, don't be
		3736	annoyed when you get a brisk "this is no bug" answer and take the chance
		3737	of learning how to interpret valgrind properly.
		3738
		3739	If you need, for some reason, empty reports from valgrind for your project
		3740	I suggest using suppression lists.
		3741
		3742
		3743	=head1 PORTABILITY NOTES
		3744
		3745	=head2 WIN32 PLATFORM LIMITATIONS AND WORKAROUNDS
		3746
		3747	Win32 doesn't support any of the standards (e.g. POSIX) that libev
		3748	requires, and its I/O model is fundamentally incompatible with the POSIX
		3749	model. Libev still offers limited functionality on this platform in
		3750	the form of the C<EVBACKEND_SELECT> backend, and only supports socket
		3751	descriptors. This only applies when using Win32 natively, not when using
		3752	e.g. cygwin.
		3753
		3754	Lifting these limitations would basically require the full
		3755	re-implementation of the I/O system. If you are into these kinds of
		3756	things, then note that glib does exactly that for you in a very portable
		3757	way (note also that glib is the slowest event library known to man).
		3758
		3759	There is no supported compilation method available on windows except
		3760	embedding it into other applications.
		3761
		3762	Not a libev limitation but worth mentioning: windows apparently doesn't
		3763	accept large writes: instead of resulting in a partial write, windows will
		3764	either accept everything or return C<ENOBUFS> if the buffer is too large,
		3765	so make sure you only write small amounts into your sockets (less than a
		3766	megabyte seems safe, but this apparently depends on the amount of memory
		3767	available).
		3768
		3769	Due to the many, low, and arbitrary limits on the win32 platform and
		3770	the abysmal performance of winsockets, using a large number of sockets
		3771	is not recommended (and not reasonable). If your program needs to use
		3772	more than a hundred or so sockets, then likely it needs to use a totally
		3773	different implementation for windows, as libev offers the POSIX readiness
		3774	notification model, which cannot be implemented efficiently on windows
		3775	(Microsoft monopoly games).
		3776
		3777	A typical way to use libev under windows is to embed it (see the embedding
		3778	section for details) and use the following F<evwrap.h> header file instead
		3779	of F<ev.h>:
		3780
		3781	#define EV_STANDALONE /* keeps ev from requiring config.h */
		3782	#define EV_SELECT_IS_WINSOCKET 1 /* configure libev for windows select */
		3783
		3784	#include "ev.h"
		3785
		3786	And compile the following F<evwrap.c> file into your project (make sure
		3787	you do I<not> compile the F<ev.c> or any other embedded source files!):
		3788
		3789	#include "evwrap.h"
		3790	#include "ev.c"
		3791
		3792	=over 4
		3793
		3794	=item The winsocket select function
		3795
		3796	The winsocket C<select> function doesn't follow POSIX in that it
		3797	requires socket I<handles> and not socket I<file descriptors> (it is
		3798	also extremely buggy). This makes select very inefficient, and also
		3799	requires a mapping from file descriptors to socket handles (the Microsoft
		3800	C runtime provides the function C<_open_osfhandle> for this). See the
		3801	discussion of the C<EV_SELECT_USE_FD_SET>, C<EV_SELECT_IS_WINSOCKET> and
		3802	C<EV_FD_TO_WIN32_HANDLE> preprocessor symbols for more info.
		3803
		3804	The configuration for a "naked" win32 using the Microsoft runtime
		3805	libraries and raw winsocket select is:
		3806
		3807	#define EV_USE_SELECT 1
		3808	#define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */
		3809
		3810	Note that winsockets handling of fd sets is O(n), so you can easily get a
		3811	complexity in the O(n²) range when using win32.
		3812
		3813	=item Limited number of file descriptors
		3814
		3815	Windows has numerous arbitrary (and low) limits on things.
		3816
		3817	Early versions of winsocket's select only supported waiting for a maximum
		3818	of C<64> handles (probably owning to the fact that all windows kernels
		3819	can only wait for C<64> things at the same time internally; Microsoft
		3820	recommends spawning a chain of threads and wait for 63 handles and the
		3821	previous thread in each. Great).
		3822
		3823	Newer versions support more handles, but you need to define C<FD_SETSIZE>
		3824	to some high number (e.g. C<2048>) before compiling the winsocket select
		3825	call (which might be in libev or elsewhere, for example, perl does its own
		3826	select emulation on windows).
		3827
		3828	Another limit is the number of file descriptors in the Microsoft runtime
		3829	libraries, which by default is C<64> (there must be a hidden I<64> fetish
		3830	or something like this inside Microsoft). You can increase this by calling
		3831	C<_setmaxstdio>, which can increase this limit to C<2048> (another
		3832	arbitrary limit), but is broken in many versions of the Microsoft runtime
		3833	libraries.
		3834
		3835	This might get you to about C<512> or C<2048> sockets (depending on
		3836	windows version and/or the phase of the moon). To get more, you need to
		3837	wrap all I/O functions and provide your own fd management, but the cost of
		3838	calling select (O(n²)) will likely make this unworkable.
		3839
		3840	=back
		3841
		3842	=head2 PORTABILITY REQUIREMENTS
		3843
		3844	In addition to a working ISO-C implementation and of course the
		3845	backend-specific APIs, libev relies on a few additional extensions:
		3846
		3847	=over 4
		3848
		3849	=item C<void (*)(ev_watcher_type *, int revents)> must have compatible
		3850	calling conventions regardless of C<ev_watcher_type *>.
		3851
		3852	Libev assumes not only that all watcher pointers have the same internal
		3853	structure (guaranteed by POSIX but not by ISO C for example), but it also
		3854	assumes that the same (machine) code can be used to call any watcher
		3855	callback: The watcher callbacks have different type signatures, but libev
		3856	calls them using an C<ev_watcher *> internally.
		3857
		3858	=item C<sig_atomic_t volatile> must be thread-atomic as well
		3859
		3860	The type C<sig_atomic_t volatile> (or whatever is defined as
		3861	C<EV_ATOMIC_T>) must be atomic with respect to accesses from different
		3862	threads. This is not part of the specification for C<sig_atomic_t>, but is
		3863	believed to be sufficiently portable.
		3864
		3865	=item C<sigprocmask> must work in a threaded environment
		3866
		3867	Libev uses C<sigprocmask> to temporarily block signals. This is not
		3868	allowed in a threaded program (C<pthread_sigmask> has to be used). Typical
		3869	pthread implementations will either allow C<sigprocmask> in the "main
		3870	thread" or will block signals process-wide, both behaviours would
		3871	be compatible with libev. Interaction between C<sigprocmask> and
		3872	C<pthread_sigmask> could complicate things, however.
		3873
		3874	The most portable way to handle signals is to block signals in all threads
		3875	except the initial one, and run the default loop in the initial thread as
		3876	well.
		3877
		3878	=item C<long> must be large enough for common memory allocation sizes
		3879
		3880	To improve portability and simplify its API, libev uses C<long> internally
		3881	instead of C<size_t> when allocating its data structures. On non-POSIX
		3882	systems (Microsoft...) this might be unexpectedly low, but is still at
		3883	least 31 bits everywhere, which is enough for hundreds of millions of
		3884	watchers.
		3885
		3886	=item C<double> must hold a time value in seconds with enough accuracy
		3887
		3888	The type C<double> is used to represent timestamps. It is required to
		3889	have at least 51 bits of mantissa (and 9 bits of exponent), which is good
		3890	enough for at least into the year 4000. This requirement is fulfilled by
		3891	implementations implementing IEEE 754 (basically all existing ones).
		3892
		3893	=back
		3894
		3895	If you know of other additional requirements drop me a note.
		3896
		3897
2550	=head1 COMPLEXITIES	3898	=head1 ALGORITHMIC COMPLEXITIES
2551		3899
2552	In this section the complexities of (many of) the algorithms used inside	3900	In this section the complexities of (many of) the algorithms used inside
2553	libev will be explained. For complexity discussions about backends see the	3901	libev will be documented. For complexity discussions about backends see
2554	documentation for C<ev_default_init>.	3902	the documentation for C<ev_default_init>.
2555		3903
2556	All of the following are about amortised time: If an array needs to be	3904	All of the following are about amortised time: If an array needs to be
2557	extended, libev needs to realloc and move the whole array, but this	3905	extended, libev needs to realloc and move the whole array, but this
2558	happens asymptotically never with higher number of elements, so O(1) might	3906	happens asymptotically rarer with higher number of elements, so O(1) might
2559	mean it might do a lengthy realloc operation in rare cases, but on average	3907	mean that libev does a lengthy realloc operation in rare cases, but on
2560	it is much faster and asymptotically approaches constant time.	3908	average it is much faster and asymptotically approaches constant time.
2561		3909
2562	=over 4	3910	=over 4
2563		3911
2564	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)	3912	=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2565		3913
2566	This means that, when you have a watcher that triggers in one hour and	3914	This means that, when you have a watcher that triggers in one hour and
2567	there are 100 watchers that would trigger before that then inserting will	3915	there are 100 watchers that would trigger before that, then inserting will
2568	have to skip those 100 watchers.	3916	have to skip roughly seven (C<ld 100>) of these watchers.
2569		3917
2570	=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)	3918	=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2571		3919
2572	That means that for changing a timer costs less than removing/adding them	3920	That means that changing a timer costs less than removing/adding them,
2573	as only the relative motion in the event queue has to be paid for.	3921	as only the relative motion in the event queue has to be paid for.
2574		3922
2575	=item Starting io/check/prepare/idle/signal/child watchers: O(1)	3923	=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2576		3924
2577	These just add the watcher into an array or at the head of a list.	3925	These just add the watcher into an array or at the head of a list.
		3926
2578	=item Stopping check/prepare/idle watchers: O(1)	3927	=item Stopping check/prepare/idle/fork/async watchers: O(1)
2579		3928
2580	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))	3929	=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2581		3930
2582	These watchers are stored in lists then need to be walked to find the	3931	These watchers are stored in lists, so they need to be walked to find the
2583	correct watcher to remove. The lists are usually short (you don't usually	3932	correct watcher to remove. The lists are usually short (you don't usually
2584	have many watchers waiting for the same fd or signal).	3933	have many watchers waiting for the same fd or signal: one is typical, two
		3934	is rare).
2585		3935
2586	=item Finding the next timer per loop iteration: O(1)	3936	=item Finding the next timer in each loop iteration: O(1)
		3937
		3938	By virtue of using a binary or 4-heap, the next timer is always found at a
		3939	fixed position in the storage array.
2587		3940
2588	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)	3941	=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2589		3942
2590	A change means an I/O watcher gets started or stopped, which requires	3943	A change means an I/O watcher gets started or stopped, which requires
2591	libev to recalculate its status (and possibly tell the kernel).	3944	libev to recalculate its status (and possibly tell the kernel, depending
		3945	on backend and whether C<ev_io_set> was used).
2592		3946
2593	=item Activating one watcher: O(1)	3947	=item Activating one watcher (putting it into the pending state): O(1)
2594		3948
2595	=item Priority handling: O(number_of_priorities)	3949	=item Priority handling: O(number_of_priorities)
2596		3950
2597	Priorities are implemented by allocating some space for each	3951	Priorities are implemented by allocating some space for each
2598	priority. When doing priority-based operations, libev usually has to	3952	priority. When doing priority-based operations, libev usually has to
2599	linearly search all the priorities.	3953	linearly search all the priorities, but starting/stopping and activating
		3954	watchers becomes O(1) with respect to priority handling.
		3955
		3956	=item Sending an ev_async: O(1)
		3957
		3958	=item Processing ev_async_send: O(number_of_async_watchers)
		3959
		3960	=item Processing signals: O(max_signal_number)
		3961
		3962	Sending involves a system call I<iff> there were no other C<ev_async_send>
		3963	calls in the current loop iteration. Checking for async and signal events
		3964	involves iterating over all running async watchers or all signal numbers.
2600		3965
2601	=back	3966	=back
2602		3967
2603		3968
2604	=head1 AUTHOR	3969	=head1 AUTHOR
2605		3970
2606	Marc Lehmann <libev@schmorp.de>.	3971	Marc Lehmann <libev@schmorp.de>, with repeated corrections by Mikael Magnusson.
2607		3972

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